tremely large size, and the vascular processes which are developed from it and eventually give rise to the formation of the placenta (taking root, as it were, in the parental organism, so as to draw nourishment therefrom, as the root of a tree extracts it from the soil) are arranged in an encircling zone, while in Man, the allantois remains comparatively small, and its vascular rootlets are eventually restricted to one disk-like spot. Hence, while the placenta of the Dog is like a girdle, that of Man has the cake-like form, indicated by the name of the organ.
Fig. 15.—A. Human ovum (after Kölliker). a. germinal vesicle, b. germinal spot.
B. A very early condition of Man, with yelk-sac, allantois and amnion (original).
C. A more advanced stage (after Kölliker), compare fig. 14, C.
But, exactly in those respects in which the developing Man differs from the Dog, he resembles the Ape, which, like man, has a spheroidal yelk-sac and a discoidal—sometimes partially lobed-placenta.
So that it is only quite in the later stages of development that the young human being presents marked differ-
