290 BALBIANIj ON SEXUAL 



•which could not be rightly interpreted without the aid of 

 M. Balbiani's figures. 



The testis, like the ovary, may remain undivided up to the 

 commencement of the reproductive epoch, or, at an earlier 

 period, begin to exhibit its peculiar modifications. Such 

 changes are, in some cases, at first very similar to those which 

 precede the occurrence of fission, but subsequently become 

 very different, for, in the latter case, no evolution of sper- 

 matozoa follows the previous elongation and division of the 

 male organ. In the general account already given of its 

 structure, reference has been made to the remarkable striated 

 appearance which, about this time, the testis presents. 



With regard to the final exclusion of the spermatic par- 

 ticles, this, according to M. Balbiani, is probably effected by 

 the contractions of the outer membrane common to the whole 

 testis, which, eventually becoming shorter, tends to drive its 

 contents into the neighbourhood of the external orifice. As 

 the eggs do not " usually acquire their full development before 

 the separation of the two individuals at the close of the sexual 

 act,'^ it would seem that they are not actually brought into 

 contact with the spermatozoa until after copulation has 

 ceased. " After their fecundation they are successively evacu- 

 ated outwards,^' in all probability by the aperture above des- 

 cribed. But the exact moment of their exit INI. Balbiani was 

 not able to seize. " In certain species, as those of Oxytrichina 

 and Stentor, this emission is entirely effected by the third or 

 fourth day subsequent to sexual imion. In other Infusoria, 

 as Paremecium, eggs have been seen within the parent more 

 than eight days after copulation. It is highly improbable 

 that they ever escape into the interior of the body.'^ Among 

 some specimens of Stylonychia mytilus observed by him in 

 copulation, M. Balbiani, at the end of three or four days, 

 found a number of minute brilliant rounded corpuscles, de- 

 posited at the bottom of the vessels, which bore a striking 

 resemblance to the eggs still enclosed within the animal's 

 body. Similar results were obtained in the case of Stentor 

 coeruleus. 



So much, then, for M. Balbiani's researches on the pheno- 

 mena of reproduction among the Infusoria. Throughout the 

 course of the preceding resume, we have ventured to make 

 little or no comment on the large amount of new matter 

 which he has brought forward, lest in any wise we might mar 

 the high interest which must attend the simple narration of 

 the facts themselves, Such interest seems to us to be of (at 



