124 A NATURALIST ON DESERT ISLANDS. 



like division (Macrura) of the more highly organized 

 Crustacea, rather than to the true, crab-like division 

 (Brachyura), it is worth noting, that Milne-Edwards and 

 Bouvier(loc.cit,) have called attention to the fact that quite 

 different examples of hermit-crabs have been able to adapt 

 themselves to an exactly similar mode of living, and if this 

 is so, why should not Crustacea of divers other groups have 

 done the same ? Thus they quote an instance of a deep- 

 sea crustacean, which they have described under the name 

 of Cancellus parfaiti. This crustacean has adopted 

 exactly the same mode of living as Pylocheles (mentioned 

 above), and is on a superficial examination the living 

 image of it. But whereas Pylocheles has a primitive 

 symmetry, which it has preserved by lodging among 

 stones, Cancellus is a hermit-crab closely allied to the 

 genus Clibinarius * ; that is to say, it once lived in a shell 

 but in taking to the same kind of shelter as Pylocheles 

 it has recovered almost completely the symmetry it had 

 lost. Ostraconotus again, to whose reduced abdomen 

 and other characters we have already referred, suggests 

 a true crab-like ancestry. 



But these questions are too technical to continue any 

 longer ; besides, we are still left to grapple for an explana- 

 tion of the steps by which our hermit-crabs have managed 

 to extricate themselves from a life in the sea and take up 

 a permanent residence on shore. 



A naval officer is, they say, never happy until he has 

 found a shore billet ; and no more, apparently, was the 

 land hermit-crab, although he was so greatly handicapped. 

 The sailor simply walks ashore with his kit ; the crab 

 on the contrary has taken ages, not only to adapt his 

 breathing apparatus to an air-breathing existence ; but 

 he has had to make arrangements (which we may be sure 

 have taken aeons to reach their present stage) whereby his 

 offspring may be able to adapt themselves, during their 

 nursery' existence, to his present mode of life. Considering 



* Examples of which we found in hundreds on the north shores of 

 Swan Island. 



