44 A NATURAL HISTORY OF THE SEAS 



vibrations to the brain via the central nervous system, 

 and it is possible therefore that the crawfish's stridulating 

 proclivities may have some definite significance in bringing 

 the sexes together. 



The larvae of both the crawfish and flat lobster are wholly 

 unlike those of other groups, and their true identities have 

 only been discovered comparatively recently. They are 

 known to fishermen as glass crabs. 



The Snap Lobsters (A/pbeus) are small lobster-like 

 crustaceans which advertise themselves in a remarkable 

 manner. The large claw has a trigger-like arrangement 

 of its movable finger and this being suddenly released 

 produces a loud snapping sound. Dr. William Beebe 

 has recounted how certain tropic sponges were so 

 riddled with these crustaceans that the animals in their 

 agitation, on being brought to the surface, relieved their 

 feelings in what sounded like a veritable burst of Chinese 

 crackers. 



The Anomura show many features common to both 

 crabs and lobsters and the members of the group may bear 

 a superficial resemblance to either one or the other. The 

 best known are the remarkable Hermit Crabs. Nearly 

 all Hermit Crabs ensconce their soft and largely unpro- 

 tected abdominal region in the discarded shell of univalve 

 molluscs, the growth limits of the various species 

 being controlled by the sizes of the shells available. As 

 already mentioned, the shell may also be shared by 

 anemones or sponges, whilst hydroids, barnacles and 

 various worms may also figure amongst the crustacean's 

 camp followers. All the members of the group are ex- 

 ceedingly active and pugnacious. 



