234 



CHARLES R. STOCKARD 



brain at a definite developmental moment, it is subsequently 

 unable to grow out and develop normally or it may be unable ta 

 grow out at all. I have definitely inhibited development during 

 this period in a large number of experiments and have either sup- 

 pressed or modified the development of the eye. It may be con- 

 cluded that, such an organ as the eye is not only derived from a 



31 



Fig. 31 A series of diagrams indicating modifications in the lateral outgrowths 

 or budding processes of the anterior region of the central nervous system. A, 

 outlines the normal case with the optic-outgrowths shown above and followed 

 by the first, second, and third primary ventricular outgrowths of the brain. B, 

 shows the outline of a brain in which the optic outpushings were suppressed, but 

 the three brain ventricles succeeded in their lateral expansion. C, indicates the 

 opposite case in which the optic outpushings were expressed, but the three brain 

 ventricles were suppressed. This is a narrow tubular brain with eyes developed 

 from it. D, outlines the condition of complete suppression of all lateral out- 

 growths, there being neither eyes nor bulging brain ventricles. A simple tubular 

 brain. 



definitely located primordia, but must also be derived during a limited 

 moment of development. 



This time-limited opportunity for origin is probably due to a 

 growth competition between organs. The eye, not attaining a 

 maximum growth rate at its proper moment, may permit an 

 excessive growth to commence in a neighboring part and such a 

 growth may then further prevent the initial growth of the eye. 



