Die infusionsthiere, auf ibue Entwickelungs-geschichte unteb-sucht

Led by his observations on the structure and habits of the Gregarinœ to conclude that they certainly belonged to the animal kingdom, and represented, in fact, the ‘animal’ in its simplest form, he was obliged to consider what place they should hold in the zoological system. In order to decide this, it was requisite to ascertain distinctly the organization and structure of the Infusoria, and to decide whether Ehrenberg’s view, according to which all the Infusoria were furnished with a complex digestive apparatus, with male and female sexual organs, and with muscles and nerves, were correct, or whether the more rational views propounded by Focke, and especially by Dujardin, as to their much more simple constitution should be adopted. According to which the structure and organization of the Infusoria is not more complex than that of the Gregarinœ ; and most of their vital functions are performed without any special organs.

One result of Siebold’s observations, which upset Ehrenberg’s erroneous notions of the nature of certain organs which he supposed to be connected with the generative function, was to prove that a certain body described by Ehrenberg as the testis, though it had not the significance of such an organ, was nevertheless essentially related to the function of reproduction. This body was termed by Siebold the ‘nucleus,’ and it appears to form a pretty constant element of the body of most Infusoria, at any rate in one phase of their existence. “This nucleus,” says Siebold, “whose presence gives the Infusoria a resemblance to a cell, demands very special attention, inasmuch as it does not at once perish after the death of the animalcule in which it was contained. Probably,” he goes on to say, “this nucleus is subsequently developed into a peculiar animal, and, in fact, many Infusoria are only the larvœ of other animals, whose complete cycle of metamorphoses has not yet been made known.” In adducing the Euglena viridis, as an instance in which he had observed the development of the so-termed ‘nucleus,’ Siebold notices the fact of its surrounding itself with a sort of capsule or cyst, a circumstance already remarked by Ehrenberg ; and it was this notice of the occurrence of an encysting process that first attracted Dr. Stein’s attention, who had been struck by the remarkable correspondence in many respects between the motions and structure of the Euglenœ with those of the Gregarinœ. The addition in the former creature of an ‘eye-spot ’did not appear to him justly to entitle the Euglenœ to a higher rank in the zoological scale than the Gregarinœ, inasmuch as that spot has none of the attributes of an organ of vision, appearing to be nothing more than a particle of pigment. The Euglenœ moreover, and this was the point which principally struck Stein, became encysted like the Gregarinœ. He felt it necessary to inquire whether the encysting process was of the same import in the one case as in the other. Nothing appeared to support the notion, propounded by Ehrenberg, that the Euglenœ became encysted only at the moment of death ; according to all analogy he was compelled to suppose that the formation of the cyst of the Euglenœ was the commencement, of a process of propagation.

Here was a new starting point in the inquiry respecting the mode of development of the Infusoria, and from this point Stein started, and where he has arrived travelling in this path is shown in the works above cited, but chiefly in that which forms the subject of the present notice.

His attention was naturally led in the first place to the Euglenœ.

In a glass, in which were contained a great variety of ciliated Infusoria, and among them also numerous individuals of Euglena viridis, Eacus, and Edeses, he remarked after the lapse of some days the formation of a thin film on the surface of the water, composed of an interlacement of confervoid filaments and Oscillatoriœ. This film swarmed with Euglenœ, many of which had lost their beaks and crawled about with a worm-like movement among the Confervœ and Oscillatoriœ-filaments. Besides these he discovered to his great joy a great many transparent, gelatinous, or quite soft cysts, which sometimes contained only a single Euglena contracted into a globular form, sometimes two of a hemispherical form appressed together. The encysted Euglenœ proved to be still living, inasmuch as they moved about in the cysts, and if the cysts were ruptured the previously globular individuals reassumed their pristine elongated figure, and crawled about in the same manner as the other beakless individuals among the confervæ.

For what purpose was this encysting ? The cyst was evidently intended for something more than a coffin. Further observations soon showed that the encysting process of the Euglenœ had really reference to their multiplication. The process, however, appeared to be different in Euglenœ from that in the Gregarinœ, inasmuch as in the latter case two individuals are conjoined before the cyst is developed, whilst in the Euglenœ the case is formed usually around but one. For where two individuals were found enclosed in a cyst, it was at once apparent that they had proceeded from the division of an originally single individual.

Whilst thus investigating the Euglenœ, his notice was also directed to other forms of Infusoria contained in the same water, such as Paramecium aurelia, Prorodon niveus, and Holophrya discolor, the latter two of which species he frequently observed enclosed in well-defined gelatinous cysts ; and as these Infusoria belonged to quite another principal division of the class, he began to hope that the process of becoming encysted would probably turn out to be of general occurrence in the Infusory world.

This proved to be the case, and the work then proceeds to describe the way in which Dr. Stein was led to detect the connexion between Epistylis plicatilis with a species of Ehrenberg’s genus Acineta; an observation which pointed the way in his future researches. One of his earliest additional observations was that of the heterogeneous generation of Epistylis digitalis. In this species he traced first the metamorphosis of the Epistylis into an Acineta, and secondly, observed in the latter the extraordinary fact of the development and evolution of a Trichodina, a discovery which Ehrenberg has attempted to explain by the supposition that the Trichodina had been previously swallowed by the Acineta. Dr. Stein’s important researches are continued through the family of the Vorticellinœ, and his observations given upon Actinophrys, Podophrya, the genus Trichodina, and on the nature of the Opalinœ, the propagation of Chlorogonium euchlorum and Vorticella microstoma, and particularly upon the quiescent condition of the latter Infusoria ; upon Spirochona gemmipara and S. Schentenii, and upon the Acineta state of Dendrocometes paradoxus, Zoothamnium affine, &c. &c.

The concluding chapter is concerning Paramecium bursaria, Ophridium versatile, Nassula ambigua, and Glaucoma scintillons.

The bulk of this mass of original and valuable observations precludes our giving more than the above meagre outline of their purport, nor will our space allow of our making any copious extracts.

We are a little surprised to find that Dr. Stein is still inclined to retain some suspicion as to the correctness of the u more modern views, according to which the family of the Volvocinœ should be referred to the vegetable kingdom ; but, as he justly observes, however this may be, his observations will still be valuable as showing how extraordinarily near the development of the lowest plants is related to that of the lowest animals.

With respect to the development of Volvox globator, Dr. Stein’s observations agree very closely with those of Mr. Williamson and Mr. Busk, recorded in the ‘Transactions of the Microscopical Society,’ and contained in our last volume, but they add nothing to the results arrived at by those writers. And with respect to the existence of more than one mode of propagation with Volvox globator, Dr. Stein’s observations have led him to precisely the same conclusions as those at which Mr. Busk had arrived, and with which Dr. Stein appears to be unacquainted. After describing, for instance, the usual mode of multiplication by segmentation of certain of the zoospores, Dr. Stein proceeds to observe that this mode of propagation does not explain the appearance of Volvox globator in localities which had been completely dried up and afterwards refilled with water, or which had for a long time been dry land. There must, as he says, be another mode of propagation, in which germs are produced which do not suffer injury from the drying up of the water, and are capable of being dispersed through the air.

These ‘winter spores,’ as they may be termed, constitute the forms termed Volvox stellatus, which, together with V. aureus, Mr. Busk had already stated should be regarded as forms of V. globator, and as representing the ‘winter,’ or quiescent spores of other Algœ. Dr. Stein’s view of V. aureus differs somewhat from that of Mr. Busk ; he regards it as the quiescent form of a distinct species of Volvox, to which he assigns the name of V. minor. But the distinction he draws between the two does not appear sufficient to justify their separation. The chief difference, according to him, between V. globator and V. minor consists in the circumstance that in V. globator eight young colonies are produced, whilst in V. minor the number is very inconstant, varying between one and nine, most usually four. The formation of a second coat around the quiescent or gold-coloured spore is described by him, as it is figured and described in Mr. Busk’s paper.

We must now conclude our notice of this highly-valuable work, which is indispensable to those who may make the nature and development of the Infusoria the subject of study.