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TRANSACTIONS I.1YKRPOOL BIOLOGICAL SOCIETY. 



cover their backs with sponges or Ascidians, possibly as 

 disguise, more probably because such animals are 

 distasteful to the fishes that might eat the crab. 



All the crabs, as well as lobsters and shrimps, as they 

 grow larger, periodically throw off or " cast " their hard 

 shells so as to permit of expansion. This process of 

 " ecdysis " may sometimes be seen taking place in an 

 aquarium, and it is so complete that not only is the outer 

 covering of the body shed, but every limb is drawn out 

 of its hard sheath, and the coverings of the eyes and the 



Fig. XX., Young Crabs (enlarged). 



delicate feelers and gills and even the cuticular lining of 

 the stomach are all cast off. For some time after this the 

 crab remains in a feeble and defenceless condition, but 

 swollen up with water, while its new shell is forming and 

 hardening. Such " soft " crabs generally hide, and are 

 recognised as being unfit for eating. 



The life-history of the shore-crab (Carcinus mamas) is 

 interesting, and figure XX. shows two of the more 

 important free stages. The developing eggs are carried 

 about as an orange or dark brown mass underneath the 

 abdomen, and when the young animals hatch out they are 



