REVIEWS. 



On True Sexual Reproduction in the Infusoria. — Recherches 

 sur les 'phenomhies sexuels des Infusoires. Par le Docteur 

 BalbianIj 1861. 



(Concluded from jiage 196.) 



Ten or twelve hours after the commencement of copula- 

 tion, yolk-granules begm to be deposited on the outer surface 

 of the germ-vesicle^ around whicli they speedily increase in 

 number and form a homogeneous layer, •which does not, how- 

 ever, succeed in reaching the vitelline membrane ; albeit 

 that the latter Ijecomes more and more encroached upon 

 from without. Its distinctness may, at any time, be demon- 

 strated by the addition of water or acetic acid ; as may also 

 that of the germ-vesicle, even when wholly concealed by its 

 fully formed investment of yolk-substance. 



As to the germinal spot, it does not appear until a late 

 period, when a few isolated granules arise within the vesicle, 

 and coalesce to form a brilliant, rounded dot. These pre- 

 Wagnerian granules must not be confounded with the scat- 

 tered molecules above referred to, Avhich are sometimes seen 

 inside the rudimentary germ-vesicle, but in time wholly dis- 

 appear. 



At the end of four or five days the development of the 

 eggs is complete, and each, with the aid of reagents, displays 

 in a very distinct manner its characteristic elements, namely, 

 vitelline membrane, Adtellus, germ-vesicle and germ-spot. 



By the shortening of the delicate tubular membrane, 

 within whicli they are confined, the ripe eggs make their way 

 into the excretory duct, and, in their passage towards the 

 surface of the body, probably undergo fertilization. At the 

 same time the other ovarian contents unite into a single mass, 

 so that, when the reproductive period has elapsed, the nucleus 

 once more returns to its original form. 



A like development of the ova has been observed in 



