259 



(2) The urinary organs of the female are essentially 

 the same as those of the male. The two ovaries are small. 

 Each of the oviducts (Miillerian ducts) has three distinct 

 regions, namely, the anterior narrow Fallopian tube (with 

 its funnel-like opening close to the ovary), the median 

 uterus, and the posterior vaginal portion. The vaginal 

 portions of the two oviducts are united, forming the vagina, 

 which opens into the beginning of the vestibule. The 

 opening of the vestibule is the vulva ; it is ventral, in front 

 of the anus. 



Development of Mammals. 



Give a general Account of the Developmental History of the 

 Rabbit. 



The ovum is fertilised in the Fallopian tube, and, on its 

 way to the uterus, undergoes total (holoblastic) segmentation ; 

 the result is a sphere of cells (morula), some of which are 

 smaller than the others. The small cells grow rapidly 

 and form an outer layer (ectoderm) enclosing the larger 

 inner cells. That layer extends ; but the inner cells re- 

 main attached to it at one spot only (embryonal area), 

 and a large cavity is formed. This stage is the blastocyst. 



The knot of inner cells (future embryo) spreads out, 

 becomes two-layered (ectoderm and endoderm) ; the em- 

 bryonic ectoderm becomes continuous with the vesicle 

 wall ectoderm, which is lined internally by an extension 

 of endoderm. The primitive streak, medullary groove, 

 head fold, mesoderm and other parts are developed in much 

 the same way as in birds (cf. Chick, page 248); and the 

 embryo is folded off, remaining connected by a narrow 

 stalk with the extra-embryonic portion of the vesicle, 

 which is a yolk-sac without yolk (umbilical vesicle). The 

 amnion is formed mainly by the tail folds, otherwise its 

 development is as in birds. (See Chick, page 248.) 



The blastocyst becomes attached to the wall of the uterus 

 by small projections, trophoblastic villi, which arise on the 

 lower surface of the yolk-sac. As the embryo grows bigger, 

 the upper wall of the yolk-sac is pressed down until (cavity 

 obliterated) it is in contact with the lower wall, which then 

 disappears, is absorbed. Thus the upper (vascular) wall 

 becomes closely connected with the uterus wall (temporary 

 yolk-sac placenta). But the principal attachment of the 

 vesicle to the wall of the uterus is by the horse-shoe-shaped 

 patch of thickened trophoblast around the sides and hind 



