EXISTENCE OF SEXUAL PROCESSES. 233 



might well be regarded as ova, and which Balbiani, indeed, credited 

 with all the properties of such structures. 



According to Stein, who in general supported this theory, the eggs 

 develop inside the maternal body, and the resulting embryos, for 

 which he mistook the above-mentioned parasitic Suctoria, leave the 

 mother in the form of Acinetce. On the other hand, Balbiani alleged 

 that he had repeatedly observed the laying of these " eggs," and he 

 therefore regarded the Infusoria as oviparous animals. 



What still further increased the resemblance between these pro- 

 cesses, thus shortly summarised, and the phenomena of sexual 

 reproduction, was the fact that they were preceded by a veritable 

 copulation. 



Even Leeuwenhoek believed that he had seen his Infusoria 

 in the act of pairing. Other investigators, like Russworm-Gleichen 

 and 0. F. Miiller, asserted the same thing, but their results fell into 

 discredit, and were forgotten, when Ehrenberg and Dujardin explained 

 the phenomenon as a peculiar case of the longitudinal division which 

 they had so frequently demonstrated among the Infusoria. At any- 

 rate, the credit is due to Balbiani of having recognised that the con- 

 jugation of two originally distinct individuals was an actual fact. In 

 this act the two animals lie together with their mouths in contact, 

 not only superficially, as Balbiani would have it, but so intimately 

 that the connecting parts are sometimes absorbed, and the animals 

 form a double body for several days. Balbiani interpreted this as an 

 act of copulation, in which the sperms were mutually exchanged. 

 Stein 1 also recognised a distinct association between the copulation 

 and the reproduction of Infusoria, but refused to regard the act as an 

 actual fecundation. He considered it as analogous to the conjugation 

 of certain lower plants a process which seems to bring to maturity 

 the hitherto inactive and undeveloped sexual organs, or so to change 

 them that a subsequent (self) fertilisation 2 becomes possible. He 

 supports this opinion by observations, according to which the sperms 

 became ripe as a rule, only after the separation of the conjugating 

 individuals a fact in direct antagonism to the theory of actual co- 

 pulation. He further cites cases in which the conjugation (" Syzygie," 

 Stein) leads to a complete and inseparable union of the two individuals. 



These relations began to assume a somewhat changed complexion 

 in the light of the facts advanced by Bittschli, which excluded any com- 

 parison with the processes of sexual reproduction, and furnished new 



1 At least in the second volume of the researches above referred to. 



2 It is striking that Stein speaks only of a fertilisation of the nucleus of the embryonal 

 sphere, which performs the functions of an ovary, and not of the egg-like bodies which 

 result from this by segmentation. 



