STRUCTURE .OF THE OVUM OF THE BIRD. 183 



ment in size, soon assume the form of bright polygonal bodies, 

 and then of small spheroids of thoroughly homogeneous ap- 

 pearance, in which no cell membrane can be demonstrated ; 

 for the membrane that appears on the larger spheroids after 

 the addition of water can scarcely be regarded as the equiva- 

 lent of a cell membrane. These small polygonal and round 

 vitelline corpuscles are very resistant; when flattened with the 

 covering glass, they exhibit a stellate, streaky, fractured surface, 

 and their reactions, that have recently been studied by His, show 

 that they belong to the protagon-containing class of substances. 

 Ultimately these spheroids attain very extraordinary dimen- 

 sions ; but we may trace the passage of the smallest corpuscles 

 step by step into the largest. In the interior of larger spheroids 

 one or more of the smaller corpuscles may be constantly 

 found, and within these, again, are frequently others of still 

 smaller size. M. His (53) rests upon this fact his view that the 

 vitelline spheres are cells, whilst the corpuscles enclosed in 

 them are nuclei and nucleoli. Nevertheless, their form, their 

 instability, their firm consistence, the gradual passage of the 

 smaller into the larger spheroids, the circumstance that as the 

 follicles advance to maturity the number of small spheroids 

 diminishes, whilst the larger increase, all concur to make me 

 disagree with His's interpretation. Nor am I more disposed to 

 concur with Gegenbaur in believing that an endogenous 

 development of the smaller spheroids takes place in the 

 interior of the larger. I think it is more probable that the 

 smaller spheroids are simply forced into the interior of. the 

 larger, since the latter are of much softer consistence ; whilst 

 in every movement of the yolk the .closely compacted 

 elements of which it consists must be subjected to mutual 

 pressure. The larger spheroids seem to proceed from the 

 smaller by a simple process of imbibition of fluid. V. Wittich 

 (128) has arrived at similar conclusions in respect to the ova 

 of the Arachnida ; the spheroids of the yolk are here not true 

 cells, and they enlarge in consequence of the imbibition of the 

 surrounding fluid albuminous substance. The yellow yolk, 

 rhich subsequently constitutes the principal mass of the egg, 

 the Reptile and of the Bird, is only a modification of the 

 ; and he describes in particular the larger vitellme- 



