98 REPORT OF COMMISSIONERS OF INLAND FISNERIES. 



is usually severed from the body as the result of an injury of the ap- 

 pendage. This leads to the conclusion that the high perfection of the 

 power of regeneration at the breaking plane as compared with other 

 levels, either distal or proximal to it, is causally connected with the 

 liability to injury and, consequently, upon the basis of evolutionary 

 principles, is the result of natural selection. 



In this connection another observation may be cited, viz.: in some 

 crustaceans, especially the crayfish and crab, and the same is also 

 true in the lobster, the swimmerets are slower in restoration than the 

 thoracic appendages. Some writers have suggested that the supply 

 of food material is an important factor in producing this comparative 

 difference ; but the following experiment would indicate that such a 

 factor should not be given too great importance in explaining this 

 difference. 



The results obtained in the following experiment illustrate one of 

 a number of similar observations. In lobster No. 100, Table II, the 

 first right leg and the first right swimmeret were removed on the same 

 date, July 25th. The leg was cut at the middle of the basal segment 

 or basiopodite, and the swimmeret was removed at its base. The 

 next moult occurred two and one-half months after mutilation. The 

 leg then showed no distinct regeneration, while the swimmeret was 

 n-estored to about three-fourths the normal size. In such a case it is 

 •-evident that, though the leg was more favorably situated than the 

 swimmeret, with reference to the source of food material, its regener- 

 ation was less rapid. In passing it might also be observed that if 

 the leg in this experiment had been removed a quarter of an inch 

 farther out, i. e., at the breaking plane, it would have regenerated 

 very rapidly (see page 96), although in that case the supply of food 

 material would, if anything, be even less. In conclusion, then, it may 

 be said that, so far as the present observations go, the results indicate 

 that some factor or factors, other than the supply of food material, 

 determine the difference between the power of regeneration of the 

 swimmerets and that of the thoracic appendages. 



