( 7 ) 



In the "case of Paoiiyopsis typica the association with a colonial sea- 

 anemone of a genus related to Mamilli/era is even more remarkable. Here 

 there is no shell to play the part of " Sir Pandarus of Troy," but the sea- 

 anemone settles upon the hinder part of the young hermit-crab's tail, and 

 the two animals grow up together, in such a way that the spreading 

 zoophytes form a blanket which the hermit can either draw completely 

 forwards over its head or throw half-back, as it pleases 



In all these cases the happy results of commensalism are finely illus- 

 trated ; for each animal, without exacting anything for itself, gives the 

 other signal assistance — the zoophyte by protecting and masking the hermit- 

 crab, the hermit-crab by continually carrying the zoophyte to rich pastures. 



Though the typical Paguroid lives in a spiral shell, and bears its story 

 in its tail, various other means of protection are employed by hermit-crabs. 

 For instance, the members of the small family of perfectly symmetrical 

 hermit-crabs. Pyloche/idce, hardly ever use a spiral shell ; but either occupy 

 holes in stones, or take sanctuary in living sponges, or impact themselves 

 in tubes of water-logged (sunk) bamboo or mangrove, or occasionally in a 

 tooth-shell, always closing the orifice of ingress with their stopper-like 

 chelae. Xylopa^urus also shelters in sunken reeds and bits of wood, and 

 several species of Cancellus find an asylum in holes in sponge and rock In 

 Xvlopa^uviis and Cancellus, as already mentioned, the abdomen is straight 

 and appears to be symmetrical ; but that the symmetry is only secondarily 

 acquired and superficial, and that these forms are descended from an ordinary 

 asymmetrical stock, is proved by the fact that the posterior abdominal 

 appendages — though present only in the female — exist only on the left side. 



Certain forms which hide in holes do not regain even an apparent 

 symmetry, such are the species of Pagurisles that hides in living sponge, and 

 the Troolopaguriis that lives in small holes in coral. 



Some of the land-hermits of the genus Coenobita out-grow the accommo- 

 dation that, with due regard to portability, is afforded by a moUuscan 

 shell, and will use instead the husk of a fruit, or a piece of cocoanut shell, or 

 even the bottom of a bottle. 



Besides the Lithodidce, a few true hermit-crabs, either on account 

 of their large size, or by adaptation to particular conditions of life, are 

 independent of foreign protection ; such are Bir^iis, Porcellaiiopa^uias, the 

 persistent larval forms known as Glaucothoc, and perhaps also Tylaspis and 

 Ostraconotus. 



Intermediate between these perfectly independent forms, and those which 

 borrow, or burrow, stands the remarkable Papjiropsis, already mentioned, 

 which though free is under contract for life, like the citizen of a state. 



