58 



DEVELOPMENT OF THE FROG'S EGG 



[Cm. V 



bottom (Fig. 20, C). The lateral sense-plate is split into an 

 anterior and posterior part on each side. The more anterior 

 part may still be called the sense-plate, SP, and the posterior, 

 the gill-plate, GP. 



Fig. 20. — Surface views of young embryo of Rana. (After Schultze.) IM. Inner 

 medullary plate. EM. Outer medullary plate. GP. Gill-plate. SP. Sense-plate. 

 BP. Blastopore. 



A later stage is shown in Fig. 20, D. Here the sense-plate 

 is found to have extended laterally and forward, and the two 



