40 UNIVERSITY OF MISSOURI STUDIES [328 



Later investigation has not substantiated this view. Mor- 

 gan, from his experiments upon the hermit crab, which have 

 been mentioned in an earher part of this paper, was led to take 

 a precisely opposite ground in regard to the relation of regener- 

 ating capacity to the physiological importance of the part con- 

 cerned and its liability to injury. He found that the hermit crab 

 was capable of regenerating any appendage that was removed, 

 even though under natural conditions, the possibility of injury 

 to the appendage, as in the case of the abdominal appendages 

 which are not exposed, was practically precluded. 



He also found that appendages frequently injured regener- 

 ated not only at the usual breaking joint, but were capable of 

 regenerating from a point either above or below that level. 

 From these observed facts he concludes that for the hermit-crab 

 at least, there is no relation whatever between power of regener- 

 ation and liability to injury. Not only for the hermit crab, but 

 for all other animals that are capable of regeneration, he denies 

 the existence of any such relation. 



My own observations upon the crayfish tend to substantiate 

 Morgan's view. I have found that appendages do regenerate 

 which under normal conditions are not usually injured, and that 

 they are capable of regenerating from levels other than that of 

 the usual breaking joint. In my paper on The Crayfish of Mis- 

 souri ( :02) I mentioned the extreme uniformity of parts in 

 C. gracilis, a species which spends nearly its entire life in bur- 

 rows and is therefore protected from injury. 



This uniformity shows that the appendages are seldom or 

 never injured under normal conditions. In only one instance, 

 and that has been since the above paper was written, have I 

 ever found an adult of C. gracilis that had lost an appendage. 

 Yet I found that when young individuals of this species were 

 used for experiment, new appendages were restored as fre- 



