336 



A. W. BELLAMY. 



tant limiting factor in the experimental control of modifications. 

 The range of variation in this respect seems to be widest during 

 the early cleavage stages. In the great majority of experiments, 

 while one usually finds a complete series of stages from nearly 

 normal to the most extreme deviations from the normal, the 

 modifications produced tend to conform to certain types, varying 

 with the physiological condition of the eggs and the treatment 

 they receive. It is therefore necessary to speak in terms of 

 averages in discussing a given type of abnormality. 



In general, as the concentration of a given chemical to which 

 the eggs are exposed, is increased, or with longer exposure to the 

 same concentrations, the modifications produced become more 

 extreme. They are discussed in the order in which they appear. 



(a) Retardation of the Dorsal Lip Region. These are stages 



FIG. 15. Inhibition of the dorsal lip region after 38 hours exposure to m/io.62 

 LiCl. Eggs placed in the solution were in 16 32-cell stages 24 hours after deposi- 

 tion. (Experiment IV 76.) d.L, dorsal lip region; y.p., yolk plug. 



in which only the dorsal lip region seems much inhibited, al- 

 though occasionally the cleavage ratio may increase in value 

 somewhat, and the gastrular angle (see p. 329) in a small per 

 cent, of the cases may be slightly more acute than in the control 

 eggs. Where only the dorsal lip region is inhibited, the blasto- 

 pore takes the form of an inverted V or U and when complete 

 the yolk plug is oval, and may be several times longer than broad 

 in the sagittal plane. 



