( 387 ) 



often forms papillae, has still a very healthy appearance. The outer 

 wall of this bowl never disappears. In its further growth the placenta 

 reaches the edges of the bowl of the umbilical vesicle, later still it 

 grows into it and coalesces with the inner wall: the sinus terminalis 

 then lies halfway the thickness of the placenta, while a fold of the 

 endoderm seems to lia\e been incorporated into it. 



In the last period of pregnancy, from the above described parts, 

 left free by the progressive and regressive processes, epithelium grows 

 between the degenerated and the normal i)art of the mucosa, perhaps 

 joins with the meanwhile jn-oliferating glandular remains in the 

 depth : the umbilical vesicle is lifted oif from the mucosa. Somewhat 

 later this begins also all round the placenta, so that at the end of 

 pregnancy this organ is more or less stalked and after parturition 

 the greater part of the uterine wall is already pi'ovided with a new 

 epithelium. 



Comparative considerations. Among Rodents the in- 

 vestigation of the times at wiiich various processes and organs of 

 the ovule (not of the foetus) are found, leads to the following series : 

 Sciurus — Lepus — Arvicola — Meriones — Mus — Cavia, in which 

 the first has retained the most primitive forms, Lepus in many 

 respects forms a transition to the last, in which more and more by 

 new processes coming to the fore, the old, primitive ones are sup- 

 planted, mixed up and altered, in a word become nearly irrecognisable. 

 Of this latter fact the study of the literature on the relation of ovule 

 and uterus in Rodents, gives sufficient evidence ; it also appears here 

 how great a support is afforded by a comparative anatomical in- 

 vestigation ; even, that various problems cannot be solved without 

 its assistance. 



The progression appears clearly in the pecularities of the umbilical 

 vesicle in the various animals: in all the upper part is invaginated 

 into the low^er, with Sciurus not until late, with Cavia the process 

 is among the first ; the distal wall always remains with Sciurus, 

 with Lepus it disappears late, with Cavia already quite at the be- 

 ginning; the endoderm covers the inner wall already very early in 

 Sciurus, very late in Mus, never entirely in Cavia. 



In the same order the antimesometral fixation and the allantoid 

 placenta occur earlier and together with these the trophoblast thickening, 

 which causes them. It is exactly the remarkable pre-placentary 

 processes which have been so carefully studied with Mus and Cavia, 

 which by this replacing present the greatest difficulties. 



With all Rodents the vegetative ovular pole becomes connected 



