EARLY DEVELOPMENT IN THE FROG. 



329 



and is intended to describe conditions where the dorsal lip is 

 retarded to a relatively greater extent than the lateral lips (Fig 

 14, A). The term "wide-crescent blastopore" refers to a condi- 

 tion where the blastopore is in the form of a broad crescent 

 (Fig. 17), and is intended to describe a condition where both 

 dorsal and lateral lips are inhibited. The term "secondary 

 invagination" describes a situation where a second infolding 



C 



D 



FIG. 8. Stages in the disintegration of eggs in an early gastrula stage following 

 several hours exposure to ml 1,000 KNC, or in m[i, 000,000 HgCh. The progress of 

 disintegration follows this general plan in all agents in concentrations that kill 

 the egg within several hours. 



takes place apical to an original equatorial blastopore (Fig. 18). 

 The "gastrular angle" is the angle between a plane through the 

 center of the egg parallel to the floor of the segmentation cavity, 

 and a line through the center of the egg and the blastopore (Fig. 

 9). Obviously, comparison of the gastrular angle of normal eggs 

 with this angle in inhibited eggs is possible only at the beginning 

 of gastrulation. 



The development of the frog is so well known that a detailed 

 description of the process is unnecessary. However, mention 

 of several features of normal development will be of use for 

 comparison with abnormal types. 



