178 OVAKY AND PAROVARIUM, BY W. WALDEYER. 



around the micropyle, like those, for example, that have been shown by 

 Buchholz to exist in the Osmerus eperlanus. In Insects they arise 

 at the point where the cell of the ovum communicates with the 

 so-called germ yolk-cells (see infra and fig. 195). Pfliiger (84) has 

 given a description of larger openings in the ova of the Cat that are 

 occupied by one of the cells of the discus proligerus, half lying within the 

 zona, and half externally amongst the epithelium of the ovum twin 

 cells or plug cells (spundzellen) of Pfliiger; in other cases he saw 

 processes of the cells of the epithelium of the ovum sticking deeply 

 in the zona pellucida. Up to the present time these observations 

 have not been corroborated by others. Where a micropyle is present, 

 it would appear to be constantly subservient to the passage of the 

 spermatozoa into the interior of the ovum. 



The principal yolk presents characters differing from those 

 of ordinary cell protoplasm. The possession of contractile 

 power has been recently observed in it by Pfliiger (84), v. la 

 Valette (117), and Strieker (114). It is remarkable that, with 

 the exception perhaps of many ganglion cells, the ovum, quite 

 independently of the secondary yolk, presents the greatest ac- 

 cumulation of cell protoplasm around a single nucleus with 

 which we are acquainted; in other words, the cells of the ovum 

 are amongst the largest uni-nucleated cells known. The pro- 

 toplasm of the egg, when fresh, is very rich in granules. M. 

 His (53) describes the -protoplasm as containing numerous 

 small granules that from their reaction appear to contain 

 protagon, and have been termed by him true yolk granules, 

 in contradistinction to the granular bodies of the secondary 

 yolk. In young mammalian ova, granules of almost every 

 variety of size are met with. The largest (fig. 193, G e) are 

 completely spherical vesicles, and resemble the yolk sphe- 

 roids of Birds; they lie scattered, as represented in the 

 figure, between the smaller granules, amongst which they 

 are directly visible. At a later period they increase in 

 number, and have so strong a lustre that scarcely anything 

 else can be seen within the zona pellucida. Their micro- 

 chemical reactions agree with those of the albuminous 

 compounds. 



The germinal vesicle appears as a sharply defined globular 

 and somewhat excentrically placed body, situated within the 



