PORIFERA, CCELENTERATA, 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 



FIG. 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 (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). 



