PORIFERA, CHELENTERATA, VERTEBRATA 103 
pig embryos. The accompanying diagram (Fig. 32) 
shows the fertilized egg and the early cleavage cells 
all alike (in black) ; some of their descendants become 
differentiated into the somatic cells of the germ 
Fic. 31.— Germ cells of vertebrates. A. From embryo of the teleost, 
Lophius, with plasmosome (?) extruded into cytoplasm. (From 
Dodds, 1910.) B. One germ cell and four somatic cells from a 
guinea-pig embryo. (From Rubaschkin, 1912.) C. Germ cell of 
chick showing ‘‘ Netzapparat.’’ (From von Berenberg-Gossler, 1912.) 
D. Primordial germ cell (g) and blood cell (6) in lumen of blood 
vessel (1) of a nineteen somite chick embryo. a = attraction-sphere. 
(From Swift, 1914.) 
layers (circles), but others (in black) remain in a 
primitive condition and are recognizable as the 
primordial germ cells ; these remain at rest for a 
considerable period, but finally multiply and become 
part of the germinal epithelium (g.ep). 
