38 



abundance of the adult forms, continual and extensive fishing 

 operations very soon affect the supply. 



10. Food of the Crawfish. 



From observations made on the crawfish in captivity, its food 

 seems to consist chiefly of any kind of animal matter that may 

 happen to be present, such as dead fish, etc., and they act as 

 scavengers in the life of the sea. They readily attack any 

 disabled fish, but are quite incapable of doing any harm to a 

 healthy normal specimen. They have frequently been ob- 

 served to make sudden and rather clumsy attacks on resting 

 fish, but these had no difficulty in escaping. It is stated by 

 some that they live to a large extent on soles, and the sugges- 

 tion has been made that the fewer crawfish the greater will be 

 the supply of soles, so that the diminution of the crawfish 

 supply is not without its compensation. This is founded 

 chiefly, I believe, on the fact that crawfish are sometimes 

 found in the fishermen's nets with a fresh sole tightly grasped 

 in their legs. From what I have seen of the habits of the 

 crawfish, however, this would appear to be the result of the 

 special opportunities for the seizing of the sole in the narrow 

 confines of the net in which both are captured. This plea, 

 therefore, for the extermination of the crawfish can scarcely 

 be justified and, in any case, is beside the point, as the regular 

 habitat of the soles of commerce is in a region far removed 

 from the haunts of the crawfish — a fact which, however, might 

 be looked upon as a confirmation of the first position. 



The stomachs of the captured crawfish frequently contain 

 a substance like finely broken-up shells and they doubtless 

 live to a large extent on various molluscs they find in the 

 mud. In captivity they seldom pay any attention to such 

 animals, but, on one or two occasions, they were observed to 

 attack fairly large and strong shells, as, for instance, that of 

 Turbo. The shell was taken up in the claws and turned round 

 so that the edge could be firmly grasped between the powerful 

 mandibles of the crawfish. The shell was then twisted to the 

 side by the legs and the piece grasped by the mandibles broken 

 off. The shell was so thick and strong that the noise of the 

 breaking could be distinctly heard through the water and 

 sides of the tank. This process was repeated until all the free 

 edge of the shell was broken off, down to the very solid oper- 

 culum, which was of course strongly drawn into the opening 

 of the shell during the process. Further progress was more 

 difficult, but, by inserting the sharp claws between the exposed 

 operculum and the shell, the contents were finally exposed. 



