The Development of the Mole (Talpa Europea), 

 the Ovarian Ovum, and Segmentation of the 

 Ovum. 



By 



"^Valter Heape, H.A., 



Demonstrator of Animal Morphology in the University of Cambridge. 



With Plate XXI. 



The Ripe Ovarian Ovum. 



The position of the ripe ovarian ovum in the ovary is 

 betraj'ed by the rounded semi-transparent Graafian follicle 

 in which it lies, projecting prominently on the surface of the 

 ovary. 



If an ovary containing such a follicle be held firmly with a 

 pair of forceps on a slide, and the follicle be pricked with a 

 needle, or better still, sharply gashed with the point of a fine 

 scalpel, the ovum spirts out on to the slide together with a 

 not inconsiderable amount of clear transparent fluid, the 

 liquor folliculi. 



In accordance with the degree of ripeness of the ovum thus 

 obtained it is more or less completely invested by a mass of 

 epithelial cells, in the midst of which it lay in the discus 

 proligerus within the follicle. 



These epithelial cells are radially arranged round the ovum 

 (fig. 1). The cells of the innermost layer are more or less 

 elongated and their inner end, tapering somewhat, rests upon 

 a thick transparent membrane which surrounds the ovum, 

 the so-called zona radiata (the zona pellucida of the older 

 observers). 



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