PORIFERA, CCELENTERATA, VERTEBRATA 103 



pig embryos. The accompanying diagram (Fig. 32) 

 shows the fertihzed egg and the early cleavage cells 

 all alike (in black) ; some of their descendants become 

 differentiated into the somatic cells of the germ 



B D 



Fig. 31. — Germ colls 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 (h) in lumen of blood 

 vessel (I) 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). 



