2S6 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



plied directly to developmental stages, but in some cases the effects on 

 development of treatment of ova or spermatozoa preceding fertilization 

 have been determined. In certain cases genetic factors have been found 

 to be concerned in producing developmental modifications similar to those 

 resulting from experimental conditions. 



Fig. 103, A-K. — Differential inhibition of head in Fiindulus heterocUtus. A, uninhibited; 

 B, cyclopia; C, cyclopia with reduction in size of eye; D, anophthalmia; E-K, anterior views of 

 uninhibited head and various degrees of differential inhibition {A, B, E-K, after Stockard, 

 1909; C, D, after Werber, 1916a). 



EXPERIMENTS ON DEVELOPMENTAL STAGES OF FISHES 



The most conspicuous and most discussed feature of differential inhibi- 

 tion in fishes is the mediolateral differential inhibition of the head."* In 

 the inhibited heads eyes develop in all degrees of approximation to the 

 median line to complete cyclopia, reduction in size of the median eye, 

 and anophthalmia (Fig. 103). In the more extreme cases there is usually 

 reduction of the anterior brain region; but, according to Stockard, cyclopia 



'• See, e.g., Stockard, 1907a, b, 1909, 1910a, 1921, and other papers; Lewis, 1909; McClen- 

 don, 1912a, b; Werber, 1915, 1916a, b; Kellicott, 1916; Gianferrari, 1921; Hinrichs, 1925. 



