Regeneration in Comjyonnd Eyes of Crustacea 233 



to the basement membrane. Whatever differences in character 

 may exist between the hypodermal cells over different regions of 

 the eye, the results of this whole series of experiments suggest the 

 inference that presence or absence of a maximum amount of the 

 optic ganglion is a controlling factor in determining the character 

 of the regeneration. The fact that no regeneration takes place 

 from levels intermediate between a-h and c-d is in itself evidence 

 that internal conditions are different at these intermediate levels 

 than from a higher or a lower level. So far as the optic ganglion 

 may be a controlling factor the difference in conditions may be due 

 either to a difference in the character of the ganglion cells or to the 

 reduced ganglionic mass. From the structure of the optic gan- 

 glion (Parker '90 and Kenyon '97) it is probable that not until the 

 lower level c-d has been reached have the peripheral terminations 

 of the optic nerve fibers been seriously interfered with. Both 

 Parker and Kenyon mention the fact that a part of the optic nerve 

 fibers have their cellular origins located in the brain. The fact 

 that this heteromorphic appendage never regenerates except from 

 this lower level suggests that there may be a causal connection 

 between the regeneration of the heteromorphic appendage and the 

 destruction of the distal terminations of the optic nerve fibers. 

 With their peripheral terminations destroyed there might probably 

 be a tendency on the part of the optic nerve fibers to grow outward 

 and form new terminations. Since their natural terminations, the 

 cells of the optic ganglion have been destroyed it seems probable 

 that the fibers of the optic nerve stump would behave like those in a 

 nerve stump of an ordinary appendage, e.g., a leg or antenna. 

 This in itself might have a tendency to induce any new tissue that 

 regenerated to differentiate into the form of some sort of append- 

 age. 



That this heteromorphic appendage should be antenna-like in 

 form seems probable for two reasons. First, it is the natural 

 tendency of all Arthropod structures to divide into segments. 

 Second, the simplest form of joint found in any appendage is in 

 the antenna. Further, this appendage, although antenna-like, 

 shows a much greater variety in form than any ordinary regener- 

 ated appendage and the joints formed are often irregular and 



