328 A. W. BELLAMY. 



cells in certain regions of the embryo, such, e.g., as the tail bud, 

 optic vesicles, nasal pits, ventral suckers, and other rapidly 

 growing regions. 



These data on disintegration are in agreement with the data on 

 differential inhibition, acclimation, and recovery ,[in showing that 

 certain parts of the egg and embryo are more susceptible than 

 other parts, and that these differences in susceptibility have a 



-m m- 



FIG. 7. Camera lucida drawing of an egg showing disintegrated cells (white) 

 following 24 hrs. exposure to m/i,ooo KNC and 24 hrs. to m/5,ooo KNC, from a 

 two-cell stage. The animal pole is in the center of the figure. (Experiment 

 KNC. B 3 .) 



definite relation to the polar axis and to the plane of bilaterality 

 in the early cleavage stages and to other physiological axes 

 arising later in development. The significance of differential 

 susceptibility is discussed later, (pp. 346-349). 



2. Experimental Modification of Development. 

 For the sake of convenience in description, certain arbitrary 

 terms have been used to designate different "types" of abnor- 

 malities. The differential inhibition of the cleavage ratio in 



/ size of animal pole cells \ . 



earlv development I T r~ ) is expressed as 



\size ot vegetative pole cells/ 



a fraction whose denominator is ten. For example, the expres- 

 sion "cleavage = 7/10" means that the size of the animal pole 

 cells is to the size of the vegetative pole cells, as 7 is to 10. The 

 expression ''V-shaped blastopore" refers to a condition where 

 the blastopore takes the shape of an inverted "V" or "U," 



