The Male Genital System of the Scorpion, Buthus quinquestriatus

With one plate (fig. 5)

THE male genital system of scorpions, in general, has been described by several authors, e.g. Dufour (1856) and Pavlovsky (1915, 1917, 1921). However, the accounts available in the writings of these authors are neither precise nor complete. In this paper I wish to contribute a detailed study of the male genital system of Buthus quinquestriatus (H.E.), which is the commonest Egyptian scorpion. It has not been investigated by any of the previous authors.

The material used for this study was collected near Cairo and brought to Edinburgh for investigation in the laboratories of the Institute of Animal Genetics, University of Edinburgh.

Some specimens were preserved in 70% alcohol for dissection while others were fixed immediately after being captured in hot Bouin’s, Carl’s, Carnoy’s, and Sanfelice’s fluids. Of these fixatives, Sanfelice’s gave the most satisfactory results for demonstrating the different stages of spermatogenesis in the wall of the seminal tubes.

In dehydration, absolute alcohol and xylene were avoided, since they render the chitinous organs very hard and impossible to cut into serial sections. Clearing was done in methyl benzoate and benzene, and embedding in hard wax containing ceresin and stearic acid. The dyes used were Heidenhain’s and Ehrlich’s haematoxylins with eosin as a counterstain. Chlorazol black was also used for staining the chitinous organs, as recommended by Cannon (1937, 1941).

The male genital system of B. quinquestriatus (fig. i, A) consists mainly of two testes, from each of which emerges a vas deferens. This leads to a series of accessory organs attached to an ejaculatory organ which unites anteriorly with the corresponding one to form a very short common chamber opening ventrally to the exterior. The male genital opening is situated posteriorly between the two genital opérenla, which are considered by previous authors (see Abd-el-Wahab, 1952) as the appendages of the first mesosomatic segment.

Each testis (fig. 1, A) is composed of several slender tubules which intercommunicate with each other to form a ladder-like structure, which is lodged between the inferior lobules of the hepatopancreatic gland (‘liver’), in the region of the last five mesosomatic segments. In each testis there are two longitudinal tubules and four transverse ones, anastomosing with each other in such a manner that three quadrilateral meshes are formed. One of the longitudinal tubules of each testis runs near the middle of the body and one along the inner border of the mesosomatic cavity. Both the longitudinal and the transverse tubules are extremely delicate, flexible, transparent, white, and of comparatively narrow and uniform calibre throughout their whole length. In section, these tubules are circular or oval in shape, measuring from about 0·2 to 0·5 mm in diameter.

The literature shows that the testes differ in structure from one species to the other and even in individuals belonging to the same species. The abovementioned account of the testes of the species under consideration is nearly similar to what was reported by Dufour (1856) on Scorpio occitanus. It differs, however, from the reports given by Duvernoy (quoted by Dufour, 1856) on S. occitanus, Pavlovsky (1915, 1921) on Buthus australis and Scorpio maurus, and Sato (1940) on Buthus martensii.

Duvernoy mentioned that the two testes of Scorpio occitanus are united in the middle, as is the case in the ovary of the female. It is probable that Duvernoy’s was an abnormal specimen, since Dufour did not find this union in more than 100 individuals of this species.

Pavlovsky (1915) found in some forms of Buthus australis two well-developed blind diverticula, one at each end of the median longitudinal tubule of each testis. He added that there may be two quadrilateral meshes instead of three in each testis. The same author (1921) reported that in Scorpio maurus the testis is not in the form of a ladder but is made only of a single longitudinal tubule provided with four blind diverticula projecting from its inner side. He added that the first diverticulum or even the first two diverticula of each testis may partially unite with the corresponding ones of the other side.

Sato (1940) gave a very brief account of Buthus martensii. He showed by figures that the testes are united by a short transverse tubule connecting the first pair of meshes.

Histologically, the wall of the testis (figs. 2; 5, 1) is made of a flattened germinal epithelium resting on a very thin basement membrane, which is followed by an extremely thin circular muscle-layer. Inside the membrana propria, the primordial germ-cells of the germinal epithelium have given rise to a large number of spermatogonia which are in the form of loose masses of small, rounded cells containing a small amount of cytoplasm and densely chromatic nuclei. Some of these masses have been replaced by spermatocytes or spermatids or spermatozoa. Each group of similar cells is enclosed by ^a thin wall in the form of a cyst. All the cysts lie closely adjacent to each other. Sometimes the cysts are partially surrounded by several degenerating cellwalls with oval nuclei.

The spermatocytes are usually larger than the spermatogonia and contain large nuclei. The spermatids form compact bundles inside their cysts. The clusters of sperm heads are surrounded by diffuse and apparently degenerate masses of cytoplasm. The spermatozoa, after becoming mature, are set free into the lumen of the testis, from which they go in clusters through the vas deferens to the seminal reservoirs.

This description of the histology of the testis is nearly similar to that of Sato (1940) in B. martensii, but differs in some respects from that of Sokolow (1913) in B. eupeus and Euscorpius carpathicus. According to Sokolow’s description, the testis is limited externally by a very high, columnar epithelium. The inner end of every cell of this epithelium stains more strongly than the rest and contains a clear vesicle. All these vesicles together form a clear border to the epithelium. The spermatogenetic cysts are scattered between the cells of the columnar epithelium.

There are two vasa deferentia, coming out from the outer angles of the foremost mesh of the testis (fig. 1, A). Each vas deferens runs forwards to join with the vesicula seminalis and the other accessory organs that will be mentioned later. It is composed of two main portions, a proximal and a distal. The proximal part is longer than the distal. It is also folded and slender, being nearly of the same calibre as the testes. The distal part is somewhat dilated. It is generally referred to as the terminal ‘ampulla’. It is absent in some scorpions such as Buthus australis and Scorpio maurus (see Pavlovsky, 1917, 1921).

The wall of the vas deferens in the proximal region is formed of cuboidal cells resting on a basement membrane ; there is a thin layer of circular muscle. In the wall of the terminal ampulla the epithelium is thrown into folds composed of cylindrical cells of different heights. The muscle-layer is more pronounced and made of intermixed circular and longitudinal muscle fibres.

The terminal ampulla of each vas deferens opens into a series of accessory organs which are generally referred to as the vesicula seminalis and the cylindrical and oval glands. The latter open directly into the ejaculatory organ.

This is a yellowish organ, nearly club-shaped in form. It is connected by it tip to the terminal portion of the dilated ampulla of the vas deferens and lies freely over the cylindrical gland and ejaculatory organ, with a slight ^c dation outwards.

It is usually filled with a large mass of spermatozoa (fig. 5, B). Its wall is comparatively thin, being made of flattened cells except near its attachment to the vas deferens, where the cells are cuboidal. The cells of the epithelium rest on a thin basement membrane; there is an extremely thin layer of interangled muscle fibres.

This gland is a transparent, white, elongated sac, nearly tubular in form. It is slightly shorter than the vesicula seminalis and lies closely over the dorsal surface of the ejaculatory organ, to which it is attached by connective tissue fibres. It is connected with the dilated portion of the terminal ampulla of the vas deferens at a point just beyond the attachment of the vesicula seminalis. Its posterior half is apparently segmented and its posterior end is bulb-like in form.

The wall of the cylindrical gland (fig. 5, B, eg) consists of a cylindrical epithelium of varying height. From the mid-dorsal surface of the posterior two-thirds of the gland, well-developed folds are produced. The musclelayer differs in thickness in the different regions of the gland. It is thick and composed of intermixed circular and longitudinal muscle-fibres.

There is a well-developed ganglionic mass (fig. 5, B, gn) situated at the extreme end of the lumen of the gland. From this mass arise lateral and median nerves running to the wall of the gland itself and that of the ejaculatory organ. This ganglion has never been recorded by any of the previous authors.

This is the most anterior gland. It is transparent, white, and nearly oval in form. It receives its contents from the terminal ampulla of the vas deferens at an opening very near to that of the cylindrical gland. It lies towards the inner side of the ejaculatory organ into which it opens. Histologically, its wall is nearly similar to that of the cylindrical gland.

Dufour (1856) referred to this organ in Scorpio occitanus as the ‘penis’ or ‘ejaculatory canal’, in the belief that this organ is used in the process of copulation. However, Birula (1910) claimed that it is not used in copulation. He discovered in S. maurus two external papillae acting as the penis during the process of copulation. Accordingly, Pavlovsky (1917) replaced Dufour’s names by the term ‘paraxial organ’, owing to the lateral position of the organ.

In the present description it is found preferable to use the name ‘ejaculatory organ’, from homology with the corresponding structures in related animals. The term paraxial organ is vague, since it can be applied to any other lateral organ in the mesosomatic cavity. Some scorpions, such as Buthus australis, B. leptochelys, B. occitanus, and the species under consideration, do not possess Birula’s papillae for copulation.

In B. quinquestriatus the ejaculatory organ (fig. 1, A, B) consists of an ejaculatory sac supported from inside by a chitinous shaft, which Pavlovsky (1921) referred to as the ‘supporting stalk’ (‘tige de soutien’).

This is an extremely elongated hollow structure which is nearly white in colour. It extends longitudinally along the inner border of the first five meso-somatic segments. It is about 15 mm long and from 1 to 2 mm broad. It is covered almost wholly by the outer border of the hepatopancreas. Its base, from the outer side, is produced slightly backwards and outwards into somewhat swollen and blind epithelial pockets, into which are inserted the basal processes of the supporting shaft (figs. 1, B; 4, B), which will be described kier.

From the inner side the base of the ejaculatory sac extends backwards as a si under, vermiform structure which is generally referred to as the flagellum (fig. i, B). This organ is folded. The proximal part of the fold is thicker and shorter than the distal one, which is in the form of a slender blind tubule coiled at its free end. According to Pavlovsky (1921) such a structure is absent from the ejaculatory sac of Scorpio maurus. It is present in most of the species belonging to the family Buthidae (e.g. Buthus australis, B. leptochelys, and B. occitanus).

The two ejaculatory sacs unite and form a comparatively short common chamber whose breadth exceeds its length (fig. 1, A). This is situated transversely and in its lumen there is a median fold projecting from the dorsal wall (fig. 5, A, fo). Ventrally the common chamber opens to the exterior by a narrow genital opening situated between the posterior margins of the genital opercula.

Opening into the common chamber from each side is a single pair of minute glands, one dorsal and one ventral, which are generally referred to as the annex glands. These yellowish glands are much branched. From their openings they extend backwards, closely adjacent to the wall of the common chamber. None of the previous authors has noticed such glands except Pavlovsky (1915) in B. australis. The function of such glands is still unknown, though it may be suggested that they secrete a substance to lubricate the vagina of the female during the process of copulation.

The wall of the ejaculatory sac (fig. 3, A, B) consists of a simple epithelium resting on a thin basement membrane. There is a thick layer of muscle-fibres. Fhe epithelium is made of cylindrical cells which differ in height in the different regions of the organ. At the places where the margins and processes of the supporting shaft are inserted, the cells are very low. The muscle-layer differs in thickness in the different regions of the ejaculatory sac. It consists OF longitudinal muscle-fibres (fig. 3, A). However, it is composed of intermixed circular and longitudinal muscle-fibres in the region of the commonchamber (fig. 3, B).

The wall of the annex gland is of the same structure as that of the ejaculatory ^Sa with the exception that its epithelium is thrown into more folds and the ¹ scle-layer is rather thin and composed entirely of circular muscle-fibres (fig 3, B).

New methods were adopted to resolve the structure of the supporting shaft. The organ was cut in serial transverse sections. Whole mounts of two kinds were also made. (i) The organ was softened in hot 4% caustic potash and examined in this medium. (2) It was dehydrated, cleared, and examined in Canada balsam.

The shaft consists of a gutter, to which are attached several processes (fig 4, A). It is a brown structure which is inserted into the lumen of the ejaculatory sac and the common chamber.

Che gutter is a trench-like, chitinous structure whose form differs in the different regions of the ejaculatory sac. In the first three-quarters of the latter, lts wall is slightly evaginated but this évagination decreases gradually back wards until it disappears. In other words, the gutter possesses two channels running close to each other in the first three-quarters (fig. 5, B) and the wall between these channels decreases gradually in height until one finds only a single channel in the last quarter (figs. 4, c, 5, D). As a matter of fact, the anterior part of the gutter has its cavity directed laterally inwards towards the opening of the oval gland, but the cavity of the remaining portion faces upwards. This different orientation of the cavity of the gutter is due to the fact that the supporting shaft in this region is slightly twisted.

In the posterior quarter of the gutter, the cavity is rather shallow (fig. 5, D), but it narrows and deepens gradually backwards towards the base of the ejaculatory sac (fig. 5, E, F), from the mid-dorsal surface of which a fold extends into the cavity of the gutter.

The outer margin of the gutter is thin and curved slightly downwards (figs. 4, c ; 5, B, D, E). It lies closely adjacent to the lateral wall of the ejaculatory sac, where the epithelium becomes very low.

The inner margin on the other hand is rather thick and divided into leaflike processes which appear in the transverse section (fig. 5, B, C) as finger-like in form. These marginal processes are inserted between the epithelial folds of the ejaculatory sac. In the last quarter of the gutter the inner margin becomes much thickened and its leaf-like processes pronounced (figs. 4, c; 5, D). At the base of the gutter the inner margin assumes the form of a thick, hard plate which is mostly smooth (fig. 5, E).

The gutter gives out anteriorly a process which runs transversely and ventrally towards the male genital opening in the common chamber (figs. 4, A; 5, A). This anterior process consists of a thick axis to which is attached a broad flap from the inner side and a narrow one from the outer side. It is suspected that these flaps form a tubular organ for transmitting the sperms from the gutter into the vagina of the female during the process of copulation.

From the base of the gutter are produced several processes of different form and size (figs, i, B; 4, A, B). TO describe these processes it is found advisable to give them new names according to their mode of orientation. They will be called the oblique vertical, the longitudinal, the outer superior, the outer inferior, the inner, and the posterior processes.

The oblique vertical process arises from the ventral surface of the gutter, at the middle of its base. It extends obliquely downwards in the form of a solid finger-like process and its tip is inserted into the ventral epithelium of the ejaculatory sac (fig. 5, E, vp).

The longitudinal process is in the form of a knife-blade which runs longitudinally backwards. It is attached from its straight edge to the ventral surface of the base of the gutter and lies horizontally with its broad surface pointing upwards (fig. 5, F, Ip). It is external to the oblique vertical process and, like the latter, is inserted into an elongated epithelial pocket of the ejaculatory sac.

Further backwards the posterior end of the gutter gives off two outer processes, namely, the superior and inferior outer processes. Both processes are leaf-like, curved, and pointed at their extreme ends. They are inserted by their tips into pocket-like protrusions of the epithelium of the ejaculatory sac (fig. 5, G). The superior outer process is divided into two unequal and narrow processes (fig. 4, B).

From the inner wall of the gutter, at the base, there extends obliquely backwards an inner process, which is the largest and most prominent of all the basal processes. It is curved and pointed. Its ventral surface is supported by a longitudinal thickening and its tip is inserted into a large epithelial protrusion of the wall of the ejaculatory sac (fig. 5, G, ip).

The posterior process extends backwards into the lumen of the flagellum. In the proximal portion of the latter it is provided with a fin-like, transparent blade (figs. 4, A, B; 5, H). In the distal portion of the flagellum it is round in cross-section. Sometimes this portion becomes twisted and in this case appears in transverse section as though made of two or three spherical bodies (fig. 5, F, G).

None of these processes, except the posterior and inner ones, has ever been recorded by any of the previous authors in any scorpion. The account of the posterior and inner processes was incomplete. In Scorpio occitanusDufour (1856) pointed out that there is a sword-like process which corresponds to the inner process of the present species. In Isometrus maculatus Pavlovsky (1917) found only two projections, which he referred to as the teeth (dents).

Pavlovsky (1921) denied the chitinous nature of the posterior process of the supporting shaft in Scorpio maurus and thus he said: ‘Elle n’est pas constituée par la chitine car au dire des investigateurs elle ne se dissout pas dans la potasse.’

In the present species, it is found that the whole of the supporting shaft loes not dissolve in caustic potash, but it stains with chlorazol black (Cannon, T37, 1941).

I wish to thank Professor C. H. Waddington, F.R.S., for providing facilities for the present investigation and for reading and criticizing the manuscript. I also wish to thank all the Egyptian collecting staff for the trouble they have taken in procuring the material for me. I am also indebted to the Editors for their criticism.