45 



and contact of the distal part of the Hmb with some point of resist- 

 ance. A glance at his figures reproduced below gives the reader 

 a better idea of his explanation than verbal description. (Figs. 1 

 and 2.) 



He maintained that the long extensor, alone, was involved in 

 autotomy, and that the break occurred cleanly, through solid 

 calcareous mtegument. 



The present writer,! in a comparative study of autotomy in 

 the Decapod group (a group admirably suited for such study, 

 because of the intense specialisation in various directions) found 

 a somewhat different explanation than that of Fredericq. This 

 was the result of a new method of analysis, viz., graphic recording 

 of the various muscle contractions, correlated with exact examina- 

 tion of the anatomy of the basal Umb-segments. 



The principles of autotomy in the walking legs of some of the 

 Macrura are the same as those seen in the more specialised 

 Brachyura. A description of self-amputation as it occurs, for 

 example, in the walking-legs of the common lobster, Homarus 

 vulgaris, will probably make explantion of the phenomenon as 

 it is seen in the shore-crab more easy. 



The average loss of legs in the lobster is comparatively small, 

 probably about 5 per cent. (Herrick) J, but the loss of walking-legs 

 alone is much smaller. In lobsters taken from the sea it is perha^DS 

 only 1 or 2 per cent. 



In a paper referring to autotomy in the crayfish, Reed § draws 

 attention to the fact that if walking legs be cut sharply by scissors 

 no autotomy occurs. She states, however, that if the legs are held 

 by the scissors the limb is usually torn off at the free joint between 

 the second and third limb-segments. I have examined this process 

 in the crayfish, and find that it agrees in every point with what is 

 described below for the lobster. 



Anyone who has even casually observed the habits of lobsters 

 in captivity or in the sea knows how effective the powerful abdominal 

 flap is in removing the animal from any source of danger. This 

 means of escape is also seen to be an essential factor in the pro- 

 duction of autotomy of the walking-legs, for, if the limb is seized 

 and crushed by strong pincers, it is usually abandoned in the 

 region of the second joint at the moment the abdominal flap occurs, 

 the basal segments at the same time being markedly extended. 



