EARLY DEVELOPMENT IN THE FROG. 



343 



Some of the experiments in which this secondary invagination 

 appeared have been cited. They are illustrated in Figs. 14, C, 

 and 1 8. Several other experiments follow. 



Experiment LiCl I. Unsegmented eggs placed in m/io. 6 

 hours: not appreciably different from control. 24 hours: be- 

 ginning equatorial gastrulation. Pigment has decreased some- 

 what in the cells of the dorsal lip region. The probable signifi- 

 cance of this djsappearance of pigment has been mentioned 

 (p. 321). 30 hours: large yolk plug equatorial gastrulse. 48 

 hours: equatorial gastrulae with secondary invaginations. 



FIG. 22. A, differential inhibition fused suckers, nasal pits, dorsal concavity. 

 Three hours' exposure (from late cleavage) to m[$ LiCl; four days in water. 

 (Experiment IV 58 b.) v.s., ventral sucker; n.p., nasal pit. B, differetnial re- 

 covery. Note the marked dorsal convexity. (Experiment IV 59 e.) Two days' 

 exposure (from late cleavage) to m/io LiCl; five days in water. 



In experiment IV 70 (see p. 337) this modification occurred 

 in about 10 per cent, of the eggs following 24 hours' exposure to 

 ra/5oo,ooo HgCl 2 and 24 hours in water. A few cases were noted 

 following 48 hours' exposure, from unsegmented, to 0.0075 P er 

 cent, formaldehyde (Experiment IV 83). In experiment R 135, 

 eggs just beginning to gastrulate were placed in o.ooi per cent, 

 formaldehyde and after 24 hours' exposure showed equatorial 

 gastrulae with secondary invaginations similar to the one shown 

 in Fig. 1 8. Eggs just beginning to segment when subjected to 

 the following graded treatment showed various degrees of this 

 modification in about 50 per cent, of the eggs: KNC m/i,ooo 

 24 hours, m/ 20,000 24 hours, 772/50,000 12 hours, m/i 00,000 12 

 hours. (Experiment KNC H 5). 



(e) The Gastndar Angle. In the normal egg the blastopore 

 normally makes its appearance in a meridian that bisects the 

 grey crescent and about 40 below a plane through the center of 



