260 CHARLES R. STOCKARD 



same environment, yet one is structurally perfect while the other 

 smaller member presents all types of deformities. The difference 

 between the two is in their developmental rate, the larger having 

 a normal rate and the smaller progressing more slowly and in 

 an arrested fashion. The depressed state of the one component 

 is the result of an inhibiting influence exerted by the other. 



11. The deformities of the small component in the double 

 individuals and the similar defects induced by stopping the devel- 

 opment of single individuals make it evident that all develop- 

 mental monstrosities are the results of simple arrest. During 

 my experiments with Fundulus eggs it has been possible to induce 

 a single type of defect with a great variety of different experi- 

 mental treatments. The reverse is also true; all varieties of 

 defects may be induced by subjecting the embryos to one and 

 the same experimental treatment. 



The primary action of all the treatments is to inhibit the rate of 

 development, and the type of deformity that residts depends simply 

 upon the developmental moment at which the interruption occurs. 

 All monsters are the result of the same cause, and the type of 

 monster depends upon the time at which the cause was in opera- 

 tion. 



Several developmental moments have been located at which 

 rather definite defects of particular organs may be induced. 

 These are the moments during which the organs are in their most 

 rapidly proliferating condition. Arresting the rate at such a 

 moment gives decidedly injurious results. When an organ is 

 developing at a slow rate the arrest fails to affect it. 



12. The development and growth of organs in the single indi- 

 vidual are interrelated in a way similar to the interrelations be- 

 tween the components of a double specimen. When one organ 

 or one component has a higher rate than another, it develops at 

 this rate for a limited time and tends to inhibit development on 

 the part of other organs. This is readily demonstrated by the 

 inhibiting effect of the growing shoot over all the potential buds 

 of a plant. When the growing tip is pinched away, the inhibited 

 buds immediately express their capacity to grow. There is 

 much evidence to indicate that a similar interaction exists among 

 the developing parts of an animal embryo. 



