No. 6.] LIABILITY TO INJURY. 291 



II. THE PERCENTAGE OF APPENDAGES LOST UNDER NORMAL 



CONDITIONS. 



The anterior end of the body is exposed when the crab is 

 moving about. This portion of the body is covered by a thick, 

 hard cuticle. The parts enclosed in the shell are softer, except- 

 ing the telson and the sixth abdominal appendages. We should 

 anticipate that the exposed portions of the body, despite their 

 greater strength, would be more often injured, and such is the 

 case. I have made an examination of a number of animals, and 

 have found that quite often one of the first three pairs of 

 walking legs has been lost. The antennae, too, are often broken 

 at the end. 



The first three thoracic legs can be thrown off near the basal 

 joint. Autonomy is known to take place also in other Decapoda 

 (see papers by Fredericq, Reaumur, Goodsir, Chantran, Brook, 

 Andrews, Herrick). This has been looked upon as an adapta- 

 tion for regeneration ! The fourth and fifth pairs of thoracic 

 legs cannot be thrown off. 



The following observations show the percentage of individ- 

 uals that have lost, under natural conditions, one or more 

 appendages. 



Of 47 individuals (collected June 12), 5 had lost one of the 

 first three walking legs. 



Of 73 individuals (June 14), 13 had lost one of the first three 



Of 68 individuals (June 1 7), 3 had lost one of the first three 

 legs. 



None of these were examined in respect to other appendages. 

 If we reduce the figures given above to percentages, we find 

 10.6, 17.8, and 4.4 per cent, respectively. That is, out of iSS 

 individuals, 21 (or 1 1 per cent) had lost an appendage. 



In order to ascertain whether the other appendages were also 

 lost, a hundred individuals were collected in September; they 

 were killed and then removed from the shells, and all the 

 appendages carefully examined. The following results were 

 obtained: 



