l6O THE EVOLUTION OF MAN. 



To the Indecidua, or lower Placenta I Animals, belong 

 t \\overv comprehensive and important vertebrate groups; 

 (1) the Hoofed Animals ( Ungulate) the Tapirs, Horses. 

 Swino, Ruminants, and others; (8) the Whale-like Mfkn&ls 

 (('ctotnoi'f'lia) the Sea-cows, Porpoises, Dolphins. Whales 

 and others. In all these Indecidua the chorion tufts are 

 distributed, singly or in bunches, over the entire surface of 

 the chorion. or over the greater part of it, They are but very 

 loosely attached to tho mucous membrane of the uterus, so 

 that the entire outer egg-membrane with its tufts might. 

 easily anil without using force bo drawn out of the depressions 

 in tln uterine mucous membrane, just as the hand is with 

 drawn from a glove. The two "vascular cakes" do not 

 really coalesce at any point of their contact. Hence, at 

 birth the "embryonic cake" (placenta fcetalis) is alone 

 removed; the "maternal cake" (placenta utfi'hnt} is not 

 displaeed. The entire mucous membrane of tho gra\i.l 

 uterus is but little altered, and, at parturition, sutlers no 

 direct loss of substance. 



Tho structure of the placenta in the second and higher 

 division of Placental Animals, tho Deciduata. is very dif- 

 ferent. To this comprehensive and very highly developed 

 mammalian group belong all Beasts of Trey and all Insect- 

 eaters. (Jnawers (AW< nt'ni^, Klophants. Hats. Semi-apes, and. 

 lastly, Apes and Man. In all those Deciduata the whole 

 surface of tho chorion is also at first thickly covered with 

 tufts. These, however, afterwards disappear from part, of 

 the surface, while they develop all the more vigorously in 

 the remainder. The smooth choriou (cltorioti l<t >;\ Fig. l!Ks, 

 chl) thus becomes distinct from the tufted chorion (chor'nnt 

 frondosum, Fig. 198, c7*/). On the former there are only 



