346 



[Proc. 



Spider-Crabs, on rocky bottoms, secured inconspicuousness by 

 decorating themselves with fragments of sponges, zoophytes, etc. ; 

 the Masked Crab secured safety by burrowing below the sand of 

 the sea bottom, and had its antennae modified to form a long 

 breathing tube ; while the Pea-Crabs lived in apparent comfort 

 inside the fortress provided by the shell of a cockle or mussel. 

 The life-story of the Edible Crab has attracted numerous workers 

 in recent years ; and it is clear that a good deal is left for future 

 investigators to inquire into. Our knowledge of spawning habits, 

 moulting, and migrations had been greatly extended, and some of 

 the new facts suggested local enquiry. Among the most interesting 

 items were those that had been ascertained as to the relations of 

 certain crabs and the common parasite Sacculina. This degenerate 

 Crustacean not only showed the effects of parasitism on itself, but 

 led to profound changes in the host; such as arrest of reproduction 

 and moulting, and the development of female characters in the 

 male crab. Recent work tended to explain these remarkable 

 results of parasitic activity in connection with the fact that the 

 Sacculina forced its host to elaborate a fatty material similar to 

 that which the normal female crab produced at the time the ovary 

 was ripening. 



Among the many devices for dealing with enemies the habit 

 of self-mutilation by discarding a leg was, perhaps, the most 

 striking. Many species of crab had a breaking point near the 

 base of the legs, and could cast off a mutilated member or one 

 that had been seized by an enemy. There was an effective 

 arrangement which secured the stopping of bleeding at the point 

 of fracture, and in course of time a new limb was regenerated. 



The lecturer concluded by suggesting local work on such 

 subjects as the attachment of eggs, migration in relation to drift, 

 and self-mutilation in species in which it is not known, also times 

 of spawning and size of crabs at time of spawning. At the 

 conclusion of the lecture the Chairman and Dr. J. K. Charlesworth 

 made a few remarks. 



