21 1] REGENERATION OF CRAYFISH APPENDAGES 23 



This was also noted by Chantran who found that nothing definite 

 could be determined concerning the regeneration previous to a 

 moult. 



In the case of the hermit crabs, experimented upon by Mor- 

 gan, apparently a moult is not necessary in order that the regen- 

 eration of the eye should become evident. At least no mention 

 is made of a moult having taken place. In his first series of ex- 

 periments, Herbst does not mention the occurrence of a moult, 

 but in his later work he distinctly states, for Sicyonia sculpta at 

 least, that two or three moults must take place before any dis- 

 tinct structure appears. He also mentions moults as having oc- 

 curred in a number of other instances. In the hermit crab Mor- 

 gan found the regenerative processes to go on very rapidly, for 

 his experiments were begun August i8 and brought to a close 

 September 15 ('98, pp. 294-5). In cases in which only the top 

 of the eye was removed, less than a month was required for the 

 regeneration of a new pigment spot, and Morgan states that in 

 some instances the pigment body was rounded and sharply de- 

 fined. Eyes of this sort when sectioned showed that the essential 

 eye structures were being regenerated. As no figures of such 

 sections are shown I am unable to judge of the progress the re- 

 generating parts had made. It scarcely seems possible that suf- 

 ficient regeneration could have taken place, in so short a length 

 of time, to enable one to form any definite conclusions as to what 

 the final outcome would be. As was mentioned before, Morgan 

 found that, after removal of the entire eye, an antenna-like 

 structure instead of an eye was regenerated. The results of 

 Herbst and Morgan differ in the fact that the regeneration was 

 more rapid, and a larger percentage of the individuals regener- 

 ated, in the case of the hermit crabs than in that of the shrimps. 

 This, however, may have been largely due to the difference in the 

 season of the year. Most of Herbst's experiments were begim 

 late in the fall or during the winter, while Morgan's were carried 



