EARLY DEVELOPMENT IN THE FROG. 



341 



not the slightest external evidence of Materiality or dorso- 

 ventrality (Fig. 20). 



Unsegmented eggs exposed 48 hours to m/l,OOO,OOO HgCl 2 

 exhibited all stages between equatorial gastrulation and fairly 



-mm..- 



Fir.. 20. 



FIG. 19. 



FIG. 19. Equatorial gastrulation following 76 hours' exposure to m/io.62 LiCl 

 from an unsegmented stage. (Experiment IV 22.3.) 



FIG. 20. Embryo radially symmetrical about the polar axis. Produced by 

 exposing unsegmented eggs 76 hrs. to m/io.62 LiCl; 20 hrs. in water. (Experiment 

 IV 22 b.) 



normal yolk plug stages. Eggs with a broad crescentic blasto- 

 pore were most prominent. The eggs died without developing 

 farther. 



Experiment IV 34. Eggs in 8-cell stage (10 hours and 20 

 minutes after deposition) were placed in w/5,ooo KMnO 4 . After 

 48 hours' exposure solution not changed the eggs showed a 

 complete series of stages from perfect equatorial gastrulse to 

 normal yolk plug stages. At this time all of the permanganate 

 had been reduced to the brown form and the solution had evi- 

 dently lost much of its toxicity. Sixty hours after being placed 

 in the solution about 50 per cent, of the embryos were elongating 

 but were markedly macrocephalic, showing differential recovery. 



(d) Secondary Imaginations. The eggs described by this term 

 show a secondary invagination appearing in a meridian bisecting 

 the original blastopore which is usually equatorial. The in- 

 vagination may extend partly or completely around the egg and 



