197] REGENERATION OF CRAYFISH APPENDAGES 9 



moval of only the upper portion, in which case the optic ganghon 

 has been but Httle or not at all injured. On the other hand, in sup- 

 port of the third conclusion, is the fact that, after removal of the 

 eye, together with the stalk, and consequently of the entire optic 

 ganglion, the only structure ever regenerated is antenna-like. 



Morgan ('98), has made a study of regeneration in the 

 hermit crab, Eupagnrtis. His experiments were made in order 

 to determine whether or not any relation exists between power 

 of regeneration and liability to injury. He first estimated the 

 percentage of appendages lost under natural conditions and 

 then carried on a series of experiments upon the different ap- 

 pendages, both those that were frequently injured and those that 

 were seldom, if ever, injured. The results of his experiments 

 led him to the conclusion that the power of regeneration and the 

 liability to injury are in no way correlated and are not causally 

 connected. 



In a second paper, Morgan ( :oo) deals with the same sub- 

 ject. The hermit crab was again used as material for experi- 

 ment and the results obtained seem to prove beyond a doubt that, 

 for the hermit crab at least, no relation whatever exists between 

 liability to injury and power of regeneration. It is well known 

 that in cases of autotomy the break occurs between the second 

 and third joints, i. e., between the basipodite and ischiopodite, 

 using Huxley's nomenclature. Normally, of course, regeneration 

 takes place from this point, but he found, however, that regen- 

 eration might take place not only at the breaking joint, but also 

 at a joint either proximal or distal to it, and not only at a joint, 

 but also from a cut surface between two joints. 



Morgan ('98) also experimented upon the eyes of the her- 

 mit crab. When the entire eye was removed, his results were the 

 same as those obtained by Herbst in the similar case. On the 

 other hand, when only a part of the eye is cut off, an eye and not 

 a heteromorphic structure is regenerated. 



