52 THE MICROSCOPE AND ITS REVELATIONS. 



which some a, a, remain unchanged, whilst others, o, o, o, o, either two, 

 four, or eight in number, are converted into ovules that appear to be 

 fertilized by the escape of the spermatozoa from the seminal capsules, 

 these being now seen in process of withering. Finally, in fig. 5, which 

 represents a Paramecium three days after the completion of the conjuga- 

 tion, are seen four complete ova, 0, o, o, o, within the connecting tube 

 m, m ; whilst the seminal capsules have now altogether disappeared. In 

 figs. 13-18 are seen the successive stages of the development of the 

 ovule, which seems at first (fig. 13) to consist of a germ-cell having 

 within it a secondary cell containing minute granules, which is to become 

 the ' vitelline vesicle.' This secondary cell augments in size, and becomes 

 more and more opaque from the increase of its granular contents (figs. 

 14, 15, 16), forming the 'vitellus' or yolk; in the midst of which is seen 

 the clear ( germinal vesicle/ which shows on its wall, as the ovule 

 approaches maturity, the ' germinal spot' (fig. 17). The germinal 

 vesicle is subsequently concealed (fig. 18) by the increase in the quantity 

 and opacity of the vitelline granules. The fertilized ova seem to be ex- 

 pelled by the gradual shortening of the tube that contains them; and 

 this shortening also brings together the scattered fragments of the-gran- 

 ular substance of the original ovarium, so as to form a mass resembling 

 that shown in fig. 1, a, by the evolution of which, after the same fashion, 

 another brood of ova may be produced. 



443. Now there can be no doubt as to the occurrence of ' conjuga- 

 tion ' among Ciliated Infusoria; and this not only in the free-swimming, 

 but also in the attached forms, as Stentor (Plate xiv., fig. 21). In 

 Vorticella, according to several recent observers, what has been regarded 

 as gemmiparous multiplication the putting-f orth of a bud from the base 

 of the body is really the conjugation of a small individual in the free- 

 swimming stage with a fully -developed fixed individual, with whose 

 body its own becomes fused. But it is doubtful whether such conjuga- 

 tion has any reference to the encysting process. According to Biitschli 

 and Engelmann, the conjugating process results in the breaking up of 

 the nucleus and (so-called) nucleolus of the conjugating individuals; 

 these individuals separate again, and after the expulsion of the broken- 

 up nuclear structures, the characteristic nucleus and nucleolus are 

 reformed. The same excellent observers adduce strong grounds for 

 distrusting Balbiani's assignment of sexual characters to the nucleus and 

 nucleolus. For although a striation may be observed on the surface 

 of the latter, no one has witnessed its subdivision into spermatozoidal 

 filaments. And if embryos are really produced at the expense of the 

 nucleus, what Balbiani described as sexual ova are really non-sexual 

 gemmules, each consisting (like the zoospore of Protophytes) of a seg- 

 ment of the nucleus surrounded by an envelope of protoplasm. There is 

 still much uncertainty in regard to the embryonic forms of Ciliate Infu- 

 soria; some eminent observers asserting that the 'gemmule ' in the first 

 instance, besides forming a cilia-wreath, puts forth suctorial appendages 

 (Plate xiv., fig. 19, A, B, c), by means of which it imbibes nourishment 

 until the formation of its mouth permits it to obtain its supplies in the 

 ordinary way; whilst others maintain these acinetiform bodies to be 

 parasites, which even imbed themselves in the substance of the Infusoria 

 they infest. 1 



1 There can be no doubt that Stein was wrong in his original doctrine that the 

 fully-developed Acinetina are only transition-stages in the development of Vorti- 

 cellina and other Ciliated Infusoria. But the balance of evidence seems to the 



