THE DEVELOPMENT OF THE EXTERNAL FORM OF THE BODY. 



179 



Fig. 87. — Mushroom-shaped embryo 

 of P. Edwardsii in the brood-cavity 

 (after v. Kennel), b, brood-cavity ; 

 e, embryo ; n, umbilical cord ; p, 

 placenta ; it, lumen of the uterus. 



embryonic and uterine placenta (Fig. 80, p. 171, and Figs. 87-89) 

 The great development of these organs 

 shows that, in the younger stages, they 

 contribute to its nourishment. They 

 degenerate later, and the embryo is 

 then, like that of P. capensis, nourished 

 by the uterine secretion. In conse- 

 quence of the close organic connection 

 of the embryo with the uterus, the 

 former is unable to shift from its 

 position. The embryo, firmly enclosed 

 in its brood-sac (Fig. 88), can only 

 move on into the vagina by the growth 

 of the parts lying between the ovary 

 and the brood-cavity itself, and by the 

 gradual absorption of the posterior 

 parts. When the embryo which lies 

 nearest the vagina passes over into the 

 latter, its brood-cavity must be com- 

 pletely absorbed before the next embryo 

 can reach the vagina. 



The extrusion of the embryos in the South 

 American species of Penpatus closely resembles 

 the passage of Insectan eggs from the oviduct 

 into the efferent apparatus. There also the 

 empty follicle left after the expulsion of the 

 -egg is completely absorbed before the next 

 ■egg is able to pass out. 



The further development of the 

 external form of the body consists 

 ■essentially in the lengthening of the 

 body, the marking off of the head and 

 trunk, and the appearance of the limbs 

 •and sensory organs. It agrees on the 

 whole in the different species, so that 

 separate accounts are here unnecessary. 



An important change in the form of 

 the young embryo is brought about by 

 the great development and marking off FlG . ss.— Embryo of p. Edwardsii in 



Of the cephalic segment from the trunk the brood-cavity (after J .v. Kennel, 



r ° _ from Langs Text-book of Comp. 



(Figs. 86 and 89). This change, which <.). e, embryo; ep, placenta. 



