Page:Popular Science Monthly Volume 84.djvu/531

Rh from the body of the mother and there is no protoplasmic connection between the two. In mammals generally, including also the human species, not a strand of protoplasm, not a nerve fiber, not a blood vessel passes over from the mother to the embryo; the latter is from the moment of fertilization of the egg a distinct individual with particular individual characteristics, and this is just as true of viviparous animals

 Nereis, showing perforatorium (P); head (H); middle piece (M), and tail (T). (From F. R. Lillie.)

Nereis. Some of the protoplasm of the egg has gathered at the point of entrance to form the entrance cone (EC) which, together with the sperm head, moves into the interior of the egg in later stages. The black spheres represent yolk. (From F. R. Lillie.)