1. Oxyphil nucleolar emissions have been found in two Tenthredinid species of two different genera. In origin the emissions are buds from the oxyphil nucleolus, and in T h r i n a x macula also from a large oxyphil body; their fate appears to be extrusion to the ooplasm.

2. Basophil material has also been found in both species, but whereas in T h r i n a x macula it originates by budding from the basophil nucleolus, in Allantus pallipes it is found as spherical bodies residual after the transformation of the early basophil nucleolus into an oxyphil nucleolus. Regarding the fate of these buds and bodies everything points to their being extruded into the ooplasm.

3. These two kinds of nucleolar emissions are elaborated practically simultaneously in Thrinax macula, but in Allantus pallipes their presence together has only been detected, so far, after the original basophil nucleolus has become transformed into an oxyphil one.

4. These observations on oxyphil and basophil nucleolar emissions, produced in the manner described under 3, appear novel in the study of insect oogenesis at least, and their nearest parallel appears to exist in the mollusc Patella.

The present work was undertaken for the purpose of determining the nature of the nucleolar buds described in a recent paper on saw-fly oogenesis (Peacock and Gresson, 20). While this paper is confined to the staining reactions and phenomena associated with the liberation of the nucleolar emissions, it is hoped, in some future contribution, to deal in some detail with yolkformation and the history of the cellinclusions during Tenthredinid oogenesis.

In studying the literature relating to nucleolar phenomena, one finds no complete summary of the more recent results in any one paper, so that it is advisable to give such in a brief statement here.

Ludford (12), working on Patella, states that the early oocyte contains an oxyphil nucleolus. As growth proceeds this increases in size and gives rise to oxyphil emissions which pass into the cytoplasm. These extrusions appear to dissolve, ‘as different fragments show various intensities of coloration ‘. At the end of the preliminary growth stage the nucleolus becomes separated into two parts, one oxyphil, the other basophil; during this process there is an extrusion of oxyphil substance into the cytoplasm. After the differentiation of the basophil nucleolus, the two parts may break up, they may remain joined, or they may separate and form distinct oxyphil and basophil nucleoli. When the yolk becomes fairly evenly distributed the two parts of the nucleolus become vacuolated and begin to disintegrate, the oxyphil part fragments and passes out into the cytoplasm leaving only a small part in the nucleus, while the basophil part disintegrates and becomes spread over the linen network.

As the early nucleolar extrusion takes place before the dispersion of the Golgi elements, Ludford suggests that the emissions may in some way prepare the cytoplasm for the activities of the Golgi elements during yolkformation.

Jörgensen’s findings (Ludford, 12) for a species of Patella differ somewhat from those of Ludford.

The nucleolus of the youngest oocytes is apparently amphophil, two kinds of emissions are given off from this, oxyphil granules and amphophil bodies which develop a basophil cap. These become scattered through the nucleus and eventually arranged peripherally as ‘Randnukleolen ‘.

Ludford (13), working onLimnaea stagnalis,foundthe behaviour of the nucleolus closely similar to that of the Patella with which he worked.

Gatenby (5), describing the oogenesis of Saccocirrus, has shown that the nucleolus gives rise to buds which pass through, and become attached to the outside of the nuclear membrane; these eventually lose their connexion and passing into the cytoplasm become broken up into granules which give rise to yolk or 1 nucleolar deutoplasm

Closely similar phenomena have been observed in many different groups; thus King records the occurrence of nucleolar buds in Peripatopsis capensis (10) and in Lithobius forficatus(9). In the former the buds have not been observed to pass through the nuclear membrane, while in the latter the young oocytes give rise to buds which pass out into the cytoplasm and 1 disappear shortly after leaving the nucleus Later, ‘the nucleolus breaks up into a number of pieces ‘, these ‘enlarge and start a process of budding ‘, the nucleolus becoming fragmented into a number of small grains. These grains increase by budding in the cytoplasm, and eventually enlarge and form yolkspheres. Nath (16) states that inLithobiusforficatus the nucleolus is at first basophil, then ‘amphophil and finally acidophil’; the nucleolar extrusions, he believes, contribute towards yolkformation.

Nath’s description for the oogenesis of scorpions (18) is worthy of note; he finds that in Euscorpius napoli and Buthus judacius the nucleolus gives rise to ‘deeply basophil bodies ‘which pass into the cytoplasm.

In these two species ordinary yolk is present (proteid in nature) but is absent from the oocytes of Palamnaeus fulvipes madraspaten sis. In the latter species no nucleolar budding takes place, in the former the nucleolar extrusions become acidophil and ‘ultimately disappear as whole bodies their substance probably taking part in yolkformation.

Nucleolar emissions have been described by several workers on insect oogenesis; thus McGill (14), for dragon-flies, states that in Plathemis lydia oxyphil bodies pass out from the basophil nucleolus; these, however, ‘dissolve in nuclear sap, and there is ground for concluding that this material undergoes a chemical change and is reprecipitated as the chromatinreticulum ‘. In An ax j unius there is only one oxyphil body which persists throughout the growth period. The basophil nucleolus represents the chromatin of the egg and during growth forms a spireme which later gives off granules which form a dense chromatin network in the nucleus.

Hogben (8), for P e r i p 1 an e t a, describes two kinds of bodies as arising from the nucleolus. The early oocytes contain a single nucleolus which is at first spherical, and as indicated by methods of staining is a plasmosome. From the early growth period this body emits small deeply staining particles, which pass through the nuclear membrane and move towards the periphery of the egg. At a certain stage vacuoles appear in the plasmosome, later they become granular and more chromatic, having a closely similar appearance to small nuclei within the nucleolus. These bodies or deutosomes pass out from the nucleolus, through the nuclear membrane and to the periphery, and at the same time it seems probable that the first type of emission ceases.

The vacuolation of the plasmosome synchronizes with the first appearance of the yolkspheres, which is preceded by the formation of vacuoles at the periphery of the egg; within some of the latter chromatin granules given off from the nucleolus were observed. Hogben concludes that true secondary nuclei are not present in this species. The deutosomes ‘break up into several homogeneous globules, which are the yolkspheres ‘, the first globules deposited at the periphery are not homogeneous but are closely similar to the intranuclear deutosomes. In certain Hymenoptera a similar process was observed ‘although no account was given, in view of the desirability of examining more favourable material with more suitable technique ‘.

Nath (17) finds that the early oocytes of Culex contain an amphinucleus consisting of a central basophil part surrounded by a plastin portion. The latter part becomes ovoid and then branches in an irregular manner; the branches fill up the nucleus and ultimately become detached from the nucleolus, which now consists of the basophil portion only. Vacuoles appear in the basophil part and its staining properties change. ‘The amount of nucleic acid in the nucleolus of the oocyte of Culex fatigans immediately after emergence from the pupa is so great that it will stain with basic dyes only.’ As the growth of the oocyte proceeds 1 the nucleinic acid seems gradually to leave first the outer portion of the nucleolus, which therefore begins to stain with acid dyes, and ultimately the central portion also ‘.

Nakahara (15), working on the silk glands of Pieris rapae and Neuronia postica, states that before the silk glands become functional portions of the nucleoli pass from the nucleus into the cell in considerable numbers, these emissions stain with acid dyes, and, he suggests, give off phosphorus as they pass from the nucleus.

Gardiner (3) describes an interesting condition in L i m u 1 u s polyphemus where the nucleolus is formed by the coalescence of bodies which pass into the nucleus. The central region is acidophile, the periphery basophil. Later, nucleolar emissions take place..

‘There is no indication that these buds are constricted off as such, it seems rather that the condition is one in which the internal pressure of the nucleolus has risen to such a degree that some of its substance is forced out—a process comparable to the bursting of a bubble.’

These spheres pass out into the cytoplasm and to the periphery, where they disappear as wholes without any fragmentation. There is a small acidophil region round each emission just before it disappears; the substance goes into solution in the cytoplasm and imports to it something which alters its staining reaction. As the result of tests on fresh and fixed material, Gardiner concludes that the nucleolus contains stores of ‘some organic substance very rich in phosphorus, and that this compound is given off to the cytoplasm during deutoplasmogenesis ‘. The compound contributes to the synthesis of the definitive yolk. Nath (19) in a recent paper on spider oogenesis finds that the nucleolus of the youngest oocyte ‘is highly basophil ‘. It increases in size and ‘develops vacuoles inside it, and becomes acidophil. It may bud off another nucleolus from it…. There are no nucleolar extrusions.’

To summarize, oocyte nucleolar extrusions are recorded as occurring in many different groups, and are believed by several workers to take part in yolkformation. These emissions are oxyphil in Patella (12) and some other forms, while in Euscorpius napoli and Buthus judacius (18) basophil buds only are present.McGill (14) believes that in Plathemus lydia the oxyphil bodies given off from the basophil nucleolus undergo a change and are ‘reprecipitated as the Chromatihreticulum while in Anax junius the basophil nucleolus gives off granules which form a chromatin network in the nucleus.

Material was obtained from specimens of T h r i n a x macula KI. and Allantus (Emphytus) pallipes Spin. (Enslin, 2); the former in April and May 1928, from pupae and adults which had passed the winter in the pupal condition, the latter from pupae and adults in June and July 1928.

The following procedure was adopted. The ovaries were dissected out under tapwater and fixed immediately in corrosiveacetic fixative. Sections 5µ in thickness were stained in Mann’s methylblueeosin. The above fixative and stain were found to be the most satisfactory, the oxyphil nucleolus being stained pink and the basophil nucleolus blue.

Material fixed by Champy-Kulľs, Da Fano’s, and Bensley’s technique, and in Bouin’s picroformol was used for comparison. Two figures are also given of sections from an adult specimen of a sister species, Thrinax mixta KI. This material was fixed in Bouin’s picroformol and stained in iron haematoxylin.

It should be remarked that the material was taken from parthenogenetic females. In Thrinax macula males have been reared, but it has been found (21) that at least two kinds of females exist, one maleproducing, the other femaleproducing. In Allantus pallipes several generations have been reared parthenogenetically without the appearance of a single male, nor have males been found in nature.

The ovarian tubes of a Thrinax macula pupa, stained with Mann’s methylblueeosin, revealed some interesting facts. Yolkformation had only just commenced in a few of the older oocytes, but all stages between this and the small recently differentiated oocytes at the proximal end of the tubes were shown.

In the early oocytes before the formation of the nutritive chambers the nuclei stain pink, while the nucleoli are basophil (fig. 1, Pl. 10). At a later stage the nucleolus has increased in size, and, at the same time, has developed a slightly oxyphil margin around the basophil part present in the older cells (fig. 2, Pl. 10). The oxyphil part increases in size and in staining properties and becomes rounded off from the other part of the nucleolus; this is shown in fig. 3, Pl. 10, taken from an oocyte which is sharply marked off from the nursecells. The two parts of the nucleolus may remain in close association for some time, or, as is more usual, become separate, the basophil part consisting of a small round body or dark granule surrounded by a faintly staining, vacuolated body which appears to vary slightly in its staining reactions, being in some cases faintly blue, while in others the acid stain seems to predominate. The basophil stain appears to become more marked in the older oocytes although, in the greater number of nucleoli examined, the outer margin seemed to be more strongly oxyphil than the remainder. The oxyphil nucleolus or plasmosome increases greatly in size, and is roughly spherical in shape (fig. 4, Pl. 10). The next stage is clearly shown by two oocytes from an ovarian tube of an adult. (It should be noted that the adult tubes, although containing fully developed eggs, also contain oocytes which are directly comparable to corresponding stages found in the pupa.) The vacuoles in the outer part of the basophil nucleolus become more marked and in some cases contain small dark granules similar in staining properties to the round basophil body from which they are apparently given off (figs. 5 and 6, Pl. 10). On examining some of the older oocytes from the pupal material, these granules were seen to increase in size, pass towards the periphery, and finally become liberated as separate bodies consisting of a basophil granule surrounded by slightly basophil material; the latter part, however, may be slightly oxyphil at the time it is liberated (fig. 7, Pl. 10). These buds may have another manner of origin as suggested by fig. 8, Pl. 10; here a large vacuolated mass is shown in contact with the basophil nucleolus from which it appears to have been derived. Granulecontaining vacuoles occur in this mass, the larger bearing a striking resemblance to buds occurring free in the nucleus and to those already described as originating from the basonucleolus. Thus it would seem that vacuolated masses may be given off from the nucleolus, and that these in turn give rise to buds containing a basophil granule.

FIG. 1.

Diagrammatic representation of nucleolar phenomena. Black and stippled = basophil nucleolus and buds. Clear outline = oxyphil nucleolus, vacuolated body, and buds.

a-h = Thrinax macula; in =Allantus pallipes.

a, original basophil nucleolus of early oocyte; b, early stage in differentiation of oxyphil nucleolus; c, later stage of same; d, oxyphil and basophil nucleolus separate, the latter now consists of a darkly staining granule surrounded by faintly staining material; e, showing formation of buds in oxyphil and basophil nucleolus; f, basophil buds free in nucleus; oxyphil buds not yet liberated; g, showing large vacuolated body which has originated from the oxyphil nucleolus; although a basophil bud is shown the vacuolated body may not be formed until a later stage; h, late stage after yolkformation. The basophil nucleolus is no longer active; the oxyphil nucleolus is still giving rise to buds; i, original basophil nucleolus of early oocyte; k, later stage diuing which the nucleolus is faintly basophil; I, later stage: the nucleolus is now oxyphil and is giving rise to buds. A basophil body is shown close to the nucleolus; m, later stage after yolkformation; oxyphil nucleolus budding; basophil body without granules present; n, showing a condition observed in many of the late oocytes, the oxyphil nucleolus appears to be breaking up.

FIG. 1.

Diagrammatic representation of nucleolar phenomena. Black and stippled = basophil nucleolus and buds. Clear outline = oxyphil nucleolus, vacuolated body, and buds.

a-h = Thrinax macula; in =Allantus pallipes.

a, original basophil nucleolus of early oocyte; b, early stage in differentiation of oxyphil nucleolus; c, later stage of same; d, oxyphil and basophil nucleolus separate, the latter now consists of a darkly staining granule surrounded by faintly staining material; e, showing formation of buds in oxyphil and basophil nucleolus; f, basophil buds free in nucleus; oxyphil buds not yet liberated; g, showing large vacuolated body which has originated from the oxyphil nucleolus; although a basophil bud is shown the vacuolated body may not be formed until a later stage; h, late stage after yolkformation. The basophil nucleolus is no longer active; the oxyphil nucleolus is still giving rise to buds; i, original basophil nucleolus of early oocyte; k, later stage diuing which the nucleolus is faintly basophil; I, later stage: the nucleolus is now oxyphil and is giving rise to buds. A basophil body is shown close to the nucleolus; m, later stage after yolkformation; oxyphil nucleolus budding; basophil body without granules present; n, showing a condition observed in many of the late oocytes, the oxyphil nucleolus appears to be breaking up.

In a last oocyte of the pupal material some buds were shown free in the nucleus and apparently moving towards the nuclear membrane (fig. 9, Pl. 10). In another oocyte they were observed close to the nuclear membrane (fig. 10, Pl. 10), but in no case were they shown passing through it or situated in the ooplasm. At this stage the latter is deeply basophil and would render the detection of the buds, if present, very difficult. Their position, however, suggests that they may pass into, or give some of their substance to, the ooplasm.

As the dark granules deriving from the basophil nucleolus are spreading through the outer part of the latter, the plasmosome enters upon a period of activity. Thus, several oxyphil bodies appear on its surface and although clearly marked off they may not become detached at this stage (fig. 6, Pl. 10). This process continues during the liberation of the basophil emissions (figs. 7 and 8, Pl. 10), and in some cases, it would appear, a large oxyphil body separates from the plasmosome. What seems to be an early stage in the formation of this body is shown in fig. 12, Pl. 10, taken from a late oocyte where a vacuolated mass can be seen originating from the oxyphil nucleolus. That this process may occur at a much earlier stage is shown by fig. 11, Pl. 10. The plasmosome and a large oxyphil body are present; a bud in close proximity to the latter suggests that these oxyphil emissions have two modes of origin—directly from the plasmosome and from the vacuolated body, the vacuoles being in all probability stages of budding. Although the basonucleolus persists as a faintly staining body usually free from granules, the basophil emissions appear to cease after yolkformation has commenced. At the same time the activity of the oxyphil nucleolus increases, oxyphil bodies being budded off into the nucleus (fig. 13, Pl. 10).

In some cases the activity is so great that the plasmosome appears to be breaking up. The oxyphil emissions spread out in the nucleoplasm and move towards the nuclear membrane, but as in the case of the basophil buds, they were not observed to pass through it. In some cases similar bodies were observed in the ooplasm, these, however, also resembled the smaller yolkglobules.

Some oocytes of the sister species Thrinax mixta stained in iron haematoxylin revealed an interesting condition; thus, in fig. 14, Pl. 10, the dark area is apparently the basophil nucleolus, while the darkly staining small bodies are buds. The other body is the plasmosome, or possibly, the oxyphil vacuolated mass. In fig. 15, Pl. 10, are shown the basonucleolus and oxyphil nucleolus, the latter budding.

The occurrence in this species of what appears to be a closely similar process to that of Thrinax macula is worthy of note. The former species was dealt with in a recent paper on saw-fly oogenesis (20), but the present contribution, however, throws new light on some of the phenomena then observed. The exact condition shown in figs. 14 and 15, Pl. 10, was not observed during the previous work.

In the early A11 a n t u s oocytes, which have not yet become separated from the adjoining nursecells, the nucleoli are basophil (fig. 16, Pl. 10). Later, they become more faintly basophil and finally oxyphil. During these changes the nucleolus does not divide into two parts, but changes as a whole from basophil to oxyphil. In the fully formed oocytes before yolkformation the nucleoli are oxyphil and in the greater number of cases show no traces of basophil nucleoli; but in a certain few an examination revealed the presence of a slightly basophil body, or bodies, containing darkly staining granules (fig. 19, Pl. 10). Thus it would appear that no large basonucleolus is present but that the basophil material is represented by these small bodies. It is difficult to explain why the latter were only shown in certain of the oocytes. They were observed in oocytes during and after yolkformation (figs. 19 and 20, Pl. 10); the presence of more than one suggests budding having taken place, but no such process was observed in this species. An oocyte in the later stages of yolkformation revealed a very interesting condition: slightly basophil bodies, without granules, were present in the nucleus and a closely similar body lay outside the nuclear membrane, the appearance and staining reaction of the body being different from that of the yolkglobules (fig. 21, Pl. 10). This is the only case in which a body resembling the basophil bodies of the nucleoli was observed outside the nuclear membrane. It is of interest to note that in most of these bodies observed in the older oocytes, granules were not present.

In the fully formed oocyte, before the formation of yolk, the oxyphil nucleolus enters upon a period of activity during which it gives rise to a number of buds (fig. 19, Pl. 10). This process continues during yolkformation (fig. 17, pl. 10) and in the later stages is usually more marked and presents the appearance of the nucleolus breaking up. In a few cases a similar condition was noted in earlier oocytes (fig. 18, Pl. 10).

These oxyphil buds pass out towards the nuclear membrane, where they may be seen in close contact with its inner surface, the membrane becoming pushed out at the point of contact. However, they were not observed to pass through the nuclear membrane.

Although many small bodies were shown outside the nucleus, it cannot be said with certainty that they were of nucleolar origin, as in this material they also closely resembled the smaller yolkglobules; but owing to the appearance of other material, and to the evidence of previous work (20), there seems but little doubt that these bodies pass into the ooplasm, where, apparently, they become indistinguishable from the smaller yolkspheres. Whether the buds subsequently disappear, or are converted directly into yolk, has not been determined.

In a recent paper (Peacock and Gresson, 20) a process of nucleolar budding was described in three species of sawflies. In Allantus pallipes the buds were described as occurring outside the nuclear membrane and it was considered that they might give rise to secondary or accessory nuclei. The present contribution does not substantiate this possibility for T h r i n a x macula and Allantus pallipes; there is no evidence that accessory nuclei are derived from either the basophil or oxyphil buds of the former species, or from the oxyphil buds and basophil bodies of the latter. But it would seem probable that one or both kinds of buds play some part in yolkformation, nucleolar activity commencing shortly before the appearance of the yolkglobules.

As previously stated, nucleolar emissions take place in several groups and in many cases are described as taking part in yolkformation. Owing to the migration of the oxyphil buds of Thrinax macula.and Allantus pallipes towards the nuclear membrane, and the manner in which they become applied to its inner surface, it seems probable that they are extruded into the ooplasm in a similar manner to that described by Ludford (12) for Patella.

These buds may be converted directly into yolk, in which case they would be difficult to differentiate from the small yolkglobules; or they may disappear as described for L i t h o b i u s f o r f i c a t u s (9). It is of interest to note in this connexion that certain small bodies in the cytoplasm resembled both the smaller yolkspheres and the nucleolar emissions.

The part played by the basophil buds is more difficult to determine; in Thrinax macula they seem to disappear before the yolk is fully formed, while in Allantus pallipes, although the basonucleolus was not shown, basophil bodies were observed in certain oocytes during the later stages of yolkformation. It is worthy of note that in some other forms a basophil nucleolus is not present in the older oocytes. Thus Harvey (6), for Lumbricus terrestris, states that a basophil nucleolus occurs in the early oogonia, and later, a plasmosome. In the older oocytes, however, the former has disappeared while the oxyphil nucleolus is still present.

As previously stated, Nath (17) records a change in the staining reactions of the basophil part of the nucleolus of Culex f a t i g a n s, and more recently (19) describes a change from basophil to oxyphil in spider oogenesis. This change is similar to that of Allantus pallipes, except that in the latter the oxyphil nucleolus does not bud off another nucleolus, and in the former ‘nucleolar extrusions ‘do not occur.

Wilson (22) points out that the staining reactions of the nucleoli ‘often vary materially at different periods in the history of the nucleus, so that the same nucleolus may be at one time oxyphilic and at another time basophilic ‘. Thus it would seem, in Allantus pallipes the nucleolus changes from basophil to oxyphil, while, at the same time, some of the original basophilic material is liberated as small granulecontaining bodies. It should be remembered that these bodies were not observed in every oocyte, so that, although they were present in certain of the older eggs, this may be an exceptional condition, their early disappearance being the more general occurrence.

The basophil buds of T h r i n a x macula and the basophil bodies of Allantus pallipes are both derived from the basonucleolus, and their behaviour in the nucleus indicates that their ultimate fate is closely similar. In the latter species, however, they are present for a longer period than in the former.

The appearance of a basophil body outside the nuclear membrane of an oocyte of Allantus pallipes points to their passing through the membrane, and the fact that this body and others in some of the later oocyte nuclei contained no granules, would seem to suggest that the latter become dissolved, the remainder of the extrusion then being utilized by the ooplasm.

In Thr i n ax macula the basonucleoli present in the oocyte after yolkformation contain only faintly staining granules, or none at all.

As already stated, Nath (18) describes ‘deeply basophilbodies ‘as originating from the oocyte nucleoli of E u s c o r - pius napo 1 i and Buthus j u d a c i u s; these pass into the cytoplasm, become acidophil and disappear as whole bodies. If the basophil emissions described in the present paper undergo a similar change, it would render their detection in the ooplasm during all stages of yolk-formation very difficult.

The basophil buds of Thrinax macula bear a certain resemblance to the accessory nuclei of Buchner (1) and others, but as such were not observed in the ooplasm, it seems more likely that these buds undergo some change and take part in yolk-formation.

The variation in the nucleolar phenomena within these two related species is not an isolated instance; thus, in insects, McGill (14) states that the behaviour of the nucleoli of P1 a t h e - mis lydia differs from that of Anax junius; while it is worthy of note that Buchner (1) finds the method of origin of accessory nuclei to vary in different species of sawflies.A variation also occurs in the behaviour of the nucleolus in scorpions (18), while Jorgensen (Ludford, 13) and Ludford (12), working on two species of Patella, record a difference in the behaviour of the nucleolar emissions.

  • 1. The material has been obtained from parthenogenetic females. In Thrinax macula at least two kinds of females exist, one maleproducing, the other femaleproducing. In Allantus pallipes males have not been found.

  • 2. In the early oocytes of Thrinax macula the nucleoli are basophil; as they increase in size they develop an oxyphil margin. Later, the oxyphil part becomes rounded off and separates from the basophil. The basophil nucleolus now consists of a small basophil body surrounded by a basophil or slightly oxyphil portion. Vacuoles appear in the outer part, and become larger, in some cases containing dark granules which probably originate from the darkly staining body. The granules increase in size and ultimately become liberated as separate bodies, consisting of a basophil part surrounded by more faintly staining material. These buds may also originate from large vacuolated masses given off from the basophil nucleolus. The buds pass towards the periphery, but were not observed in the ooplasm or passing through the nuclear membrane. They apparently disappear after yolkformation has commenced; the basonucleolus persists but seems to lose its granules.

  • 3. As the basophil buds are being formed the oxyphil nucleolus enters upon a period of activity, numerous oxyphil buds being liberated.

    In some cases the oxyphil buds originate from a vacuolated mass as large as the oxyphil nucleolus, and which arose, probably by constriction, from the latter. Oxyphil buds were observed to migrate towards the nuclear membrane.

  • 4. In Allantus pallipes the nucleoli of the early oocytes are basophil; later, they stain more faintly and finally become oxyphil. In the fully formed oocyte before yolk-formation the basophil material is only represented by small bodies containing dark granules. These bodies may be present during the later stages of yolk-formation, when in some cases they occur as basophil bodies without any granules. In one instance a similar body was observed outside the nuclear membrane.

  • The oxyphil nucleolus becomes active before yolk-formation commences; it becomes more marked in the later stages and in many cases the nucleolus appeared to be breaking up. The buds occurred in close contact with the inner surface of the nuclear membrane and, later, somewhat similar bodies were observed in the ooplasm; the latter, however, were difficult to differentiate from the smaller yolk-globules.

  • 5. The origin and behaviour of the oxyphil emissions are similar in both species. The oxyphil buds apparently pass into the ooplasm and are utilized during yolk-formation. The basophil buds of T hr inax macula and the basophil bodies of Allantus pallipes originate from the basonucleolus. The occurrence of basophil bodies without granules in older oocytes, and the presence of one body in one case outside the nuclear membrane of an Allantus oocyte suggest that these bodies lose their granules, and are then extruded into the ooplasm, where they play some part in the nourishment of the oocyte.

I wish to express my thanks to Professor A. D. Peacock, in whose department this work was carried out, for research facilities, for advice during the course of my investigations, and for supplying me with saw-flies from which my material was obtained.

Since this paper went to press some further contributions to the study of yolk-formation in the invertebrates have appeared. Por the chilopod Otostigmus feae, Nath (‘Quart. Journ. Mier. Sci.’, vol. 72) points out that the nucleolar extrusions are few in number, they ‘disappear long before the albuminous yolk puts in its appearance in the cytoplasm ‘; he concludes that they do not give rise to yolk.

On the other hand, Harvey believes that in Carsinus moenas (‘Trans. Roy. Soc. Edin.’, vol. 56, 1929) material is extruded from the plasmosome and subsequently takes part in yolk-formation; while Nath, describing the egg of the fire-fly, Luciola gorhami (‘Quart. Journ. Mier. Sci.’, vol. 73, 1929), states that the albuminous yolk arises from nucleolar extrusions. Thus the condition described in Carsinus and in Luciola adds further evidence in support of the view that nucleolar extrusions take part in yolk-formation.

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The drawings were made by means of a Zeiss camera lucida and a Watson ‘Service ‘Microscope. For figs. 1-16 a Leitz

112
objective was used, and for all others a Reichert
112
. The eyepiece was a Hawksley no. 4×10.

b b, basophil body; b g, basophil granule; & n, basophil nucleolus; bnb, basophil nucleolar bud; f c, follicle cell; I b g, large basophil granule in basophil nucleolus; nu, early nucleolus; o b, oxyphil body; o n, oxyphil nucleolus; o n b, oxyphil nucleolar bud; sp, space between follicle wall and nucleus; y, yolk.

Plate 10

All figs, from Thrinax macula; figs. 5, 6, 7, and 11 from adults, all others from pupae.

Eigs. 12 and 13 from adult of Thrinax macula; figs. 14 and 15 from Thrinax mixta adult. All other figs, from pupae of Allantus pallipes. The darkly shaded areas in figs. 12, 14, and 15, and in figs. 1722 represent more darkly stained parts of the nucleus; this appearance may be due to the action of the fixative.

Eig. 1.—Early oocyte, showing basophil nucleolus.

Eig. 2.—Later stage showing the oxyphil nucleolus arising from the basophil part.

Eig. 3.—Later oocyte which has become completely separated from the nurse-cells; the oxyphil and basophil parts of the nucleolus are distinct.

Eig. 4.—Oocyte before yolk-formation; oxyphil and basophil nucleolus; the basophil part consists of darkly staining granule surrounded by lighter part.

Eig. 5.—Later oocyte showing vacuoles, some of which contain dark granules in basophil nucleolus.

Fig. 6.—Oocyte before yolk-formation. Oxyphil nucleolus giving rise to buds; granules scattered through basophil nucleolus.

Fig. 7.—Oocyte before yolk-formation. Oxyphil and basophil nucleolus giving rise to buds.

Eig. 8.—Oocyte before yolk-formation. Oxyphil nucleolus giving rise to buds; basophil buds are shown in the ooplasm; the large vacuolated body with dark granules has probably been given off from the basophil nucleolus.