554 



ZOOLOGY 



SECT. 



of the wall of the follicle thins out and ruptures, setting free the 

 ovum which passes into the Fallopian tube. On the way along 

 the Fallopian tube impregnation takes place, and, after becoming 



II. v 



FIG. 1144. Part of a sagittal section of an ovary of a child just born. 6L r. blood-vessels ; foil. 

 strings and groups of cells derived from the germinal epithelium becoming developed into 

 follicles ; g. tp. germinal epithelium ; in. ingrowing cord of cells from the germinal epithelium ; 

 29?-. or. primitive ova. (From Hertwig, after Waldeyer.) 



enclosed in an envelope of albumen, the ovum passes onwards to 

 the uterus, there to undergo its development. 



With the absence of food-yolk are connected most of the differ- 



caps. 



ov 



dcsc 



tnemb 



FIG. 1145. Two stages in the development of the Graafian follicle. A, with the foliicular 

 fluid beginning to appear ; B, after the space has largely increased ; cajtK. capsule ; disc. 

 cumulus proligerus ; at cm. meinbrana granulosa ; or. ovum ; .sj>. space containing fluid. 

 (After Hertwig.) 



ences observable between the early stages of the development of a 

 Mammal (Fig. 1146), and the corresponding stages in the develop- 

 ment of a Reptile or Bird. One of the most striking of these is in the 

 mode of segmentation. In the case of the large ovum of the Bird, as 



