198 Mary Isahelle Steele 



processes upward into the retinulae during the embryonic devel- 

 opment. For it is not inconceivable that the innervation of the 

 ommatidia of a normal eye should be accomplished by the upward 

 growth of processes from the ganglion cells to the retinulse and 

 that in the regenerating eye it should be accomplished by proc- 

 esses growing inward from the retinulae to the ganglion cells. 

 That this is not impossible is suggested by the fact that in regener- 

 ation tissues are sometimes developed from the same germ layer 

 while they arise from different germ layers in embryonic develop- 

 ment. 



Several instances are known where muscles in regenerated 

 appendages arise from the hypodermis although normally they 

 are of mesodermal origin. Miss Reed ('04) finds this to be true in 

 the regenerating leg of the crayfish. Ost ('07) notes the same 

 phenomenon in the regenerating antennae of Oniscus. 



It is recognized, then, that certain tissues originating normally 

 from different germ layers may arise in a regenerating organ from 

 the same germ layer. It w^ould be at least possible that, although 

 the nerve connections between the optic ganglion and the retinulae 

 arise as processes from the ganglion in the development of the 

 normal eye, they might arise as processes from the retinulae in the 

 regenerating eye. As even in this case they would develop from 

 the same germ layer although from different parts of it. 



The possibility that the nerve connections may have arisen 

 differently in the embryonic eye and in the regenerating eye is 

 conceivable. Yet it seems that the evidence obtained from a 

 comparative study of the normal adult eye and the regenerating 

 eye suggests that the nerve processes develop from the retinulae 

 in the normal eye just as in the regenerating eye. 



The preceding pages show that the development of the regener- 

 ating compound eye corresponds in a general way with the embry- 

 onic development of the compound eye. They also show that the 

 observations made upon the regenerating eye do not agree entirely 

 with those of any one worker upon the embryonic development of 

 the compound eye of Arthropods. In many respects, however, 

 there is a close similarity between the development of the regener- 

 ating eyes of Palaemonetes and hermit crabs and the process of 



