192 BALlUAXIj ON SEXUAL 



existing in the ovaiy of a youug Infusorium, and, in addition, 

 a transparent circular space, very distinct from the surround- 

 ing granular ovarian mass, which has become of a greyish- 

 yellow color, under the influence of the test-liquid, j\I. 

 Balbiani infers that this space indicates the presence of an 

 internal A^esicle, but all his eflbrts to isolate it from the sur- 

 rounding tissue proved fruitless, in consequence of the ex- 

 treme delicacy of its supposed wall. 



In Chilodon, as already shown, the ovary constantly appears 

 under this simple form, merely increasing in size, and under- 

 going no further diflerentiatioii of structure. A central 

 corpuscle becomes visible Avithin the clear space, so that the 

 entire ovary of this organism presents all the parts of a single 

 Qg^, viz., outer membrane, yolk-mass, germ-vesicle, and 

 germ-spot. 



But this condition of the nucleus, which in Chilodon is 

 permanent, represents only a temporary stage of its develop- 

 ment in other Infusoria. For the solitary egg which is first 

 formed, after previous elongation, divides transversely, and 

 thus two eggs are produced. In some species this is the 

 ultimate number, but much more frequently, the process of 

 division is repeated, and, in some cases^ so often, that a long 

 chain of eggs is the final result. 



The internal vesicle is always the first part to divide, and 

 each of its halves forms a centre of aggregation for its own 

 share of the granular ovarian contents. The little rounded 

 masses which result may either forthwith separate from one 

 another, or remain connected by longitudinal commissures of 

 the granular yolk substance. The length of time during 

 which this connection is maintained, as also the diameter of 

 the commissure itself, in relation to that of the eggs between 

 which it lies, is subject to considerable variation, and hence 

 a corresponding diversity in the aspects which the repro- 

 ductive apparatus of different Infusoria presents. 



It is necessary to bear in mind that the outer membrane 

 of the ovary is not affected by the division of its contents, 

 but still continues to enclose them all; appearing in the 

 interspaces between the eggs, " sometimes as a more or less 

 narrow tube, sometimes as a slender filament. ^^ Since the 

 eggs, after their first formation, increase in size, " and acquire 

 a more abundant yolk-mass/' M. Balbiani conjectures that 

 their common envelope is, perhaps, analogous to " that por- 

 tion of the reproductive apparatus of other animals, whose 

 function it is to supply the ovules with the materials of their 

 growth and nutrition.^'' 



The following talkie, copied from M. Balbiani, well shows 



