234 THE LIFE OF CRUSTACEA 



it, its presence causes the living tissues between it 

 and the external cuticle to degenerate, so that when 

 the Crab moults an opening is left through which 

 the body of the parasite protrudes. Owing, no doubt, 

 to the drain on its system due to the presence of the 

 Sacculina, the Crab ceases to grow, and it does not 

 moult again as long as the parasite remains alive. 



r 



FIG. 76 EARLY STAGE OF Sacculina WITHIN THE BODY OF A CRAB. 

 (After G. Smith.) 



i, Intestine of the Crab ; s, body of the Sacculina, which afterwards 

 emerges on the under-surface of the Crab's abdomen ; r, roots of 

 the Sacculina. 



In addition to this arrest of growth, Sacculina 

 produces in its hosts other changes, which affect 

 chiefly the reproductive organs and the structures 

 associated therewith. Crabs of either sex infected 

 with Sacculina are incapable of breeding ; the genital 

 gland (ovary or testis) is found on dissection to be 

 shrivelled up, and the external characters indicative 

 of sex become strangely modified. The changes have 



