214 WALTEE HEAPE. 



Summary. 



The membranes surrounding the ripe ovarian ovum are two : 

 (1) a single outer, thick, zona radiata, with a granular peripheral 

 and a transparent inner portion, pierced radially by fine canals 

 through which nutriment is obtained by the ovum from the 

 follicular cells (of the discus proligerus) immediately in con- 

 tact with the zona : (2) an inner very delicate vitelline mem- 

 brane which closely covers the ovum itself; and between 

 these membranes is a space, the circum-vitelline space. The 

 confirmation of E,eichert's (No. 18), Meyer's (No. 17), and 

 van Beneden's (No. 4) observations as to the presence of the 

 inner delicate vitelline membrane appears of some interest as 

 many embryologists are still sceptical of its existence, while the 

 relation of the follicular cells with the radial canals of the 

 zona supports the view as to the source of the nutriment of 

 the ovarian ovum. On the other hand the fact that nothing 

 was seen comparable to a micropyle in the zona, such as M. 

 Barry (No. 3), and Meissner (No. 16), described, nor any 

 follicular cells within the zona such as Lindgren (No. 15), 

 von Sehlen (No. 21), and Virchow (No. 22), have observed, is 

 some further proof that the conditions of the material investi- 

 gated by these authors was abnormal. 



The yolk contained within the ovum, which is of two kinds : 

 viz. (1) homogeneous vesicular bodies, (2) minute highly 

 refractile granules, is contained within the meshes of a proto- 

 plasmic reticulum ; it is dense and contains no large globules 

 such as Beneden (Nos. 6 and 7) describes in the Bat's ova. The 

 rounded or oval nucleus contains a single centrally placed nu- 

 cleolus and a variable number of smaller or larger granules, 

 which may possibly be considered as nucleolar material. 



During maturation the vitellus becomes divided into a 

 medullary granular, and a cortical non-granular portion, the 

 circum-vitelline space between the zona radiata and the vitelline 

 membrane is enlarged, while the vitellus itself contracts away 

 from the vitelline membrane excepting (1) here and there 

 where pseudopodia-like processes connect the two, and (2) at 



