188 



KNOWLEDGE. 



[June 1, 1899. 



considered in the mass these habitations show no incon- 

 siderable variety of structure and material and position. 



In the history of evolution a very odd question arises 

 in regard to this matter. At the first thought it might 

 seem chQdish to ask whether the crustacean made the 



^^^^^t'^^^n:^. 





Plenrocrypia marginata Sars. Female in Dorsal and Ventral View 

 Breathing-plates of Female; and also detached. 



dwelling or the dwelling made the crustacean. But 

 there are instances in which we know for certain that the 

 occupant did not make its house, and yet 

 is so curiously adapted to it that we may 

 speak without extravagance of the house 

 havmg made its occupant. By making is 

 not intended original creation, but that 

 modifying which gives the creature its place 

 in classification. Take, for example, the 

 isopod Boptirm, of which the female brings 

 into the world her numerous offspring while 

 ensconced on one side of a prawn beneath the 

 carapace. Or study, in Sars' " Crustacea of 

 Norway, " the Pleurocryptu marginata, a similar 

 animal similarly situated in a Galatlua. Notice 

 in either case the rows of little dumpy ineffective 

 legs. Notice what an awkward, one-sided twist 

 the body has. Yet many of their relatives 

 have legs large and long, and capable of making 

 good play ; many of their relatives are perfectly 

 symmetrical, and so are their own small in- 

 significant husbands. But the mothers, in that 

 lying-in home which they have borrowed from 

 prawn or Galathea, close to the branchial 

 chamber of the host, where the supply of 

 wholesome water for their young is always 

 turned on, are no longer in need of wandering 

 feet. As for their figure, since they cannot 

 make the lodging exactly fit it, they let their 

 figure be canted to fit the lodging. 



Still more striking examples are afforded by 

 the hermit crabs. The name, Payunis, under 

 which Fabricius grouped them rather more 

 than a century ago, is a Greek word which 

 has been variously explained and variously 

 applied ; but, if we take it to mean, as it very well may, 

 the Fixing Tail, it will be found highly appropriate to the 

 characteristic members of this group. Everyone knows 



the general appearance of one of these hermits, a sort of 

 cross between a deformed crayfish and a periwinkle. Its 

 usual abode is the shell of some univalve mollusc. This 

 it occupies either as an abandoned tenement, free to the 

 first comer, or by picking out the original occupant, or 

 else by right of conquest over some 

 other hermit. At the approach of 

 danger or inquisitorial notice, a sus- 

 piciousness, bred perhaps of its own 

 want of scruple, bids the hermit retire 

 quite out of sight into the recesses of 

 the shell. At other times it freely pro- 

 trudes its front, with the stalked eyes 

 and antenniP, the large claws, and the 

 tips of the two long pairs of walking 

 legs. Often, as in so many other 

 crustaceans, the claws are unequal, 

 some species being commonly, so to 

 speak, left-handed and others right- 

 handed. The business of the larger 

 claw is not only to repel the foe and 

 seize the prey, but also to bar the 

 entrance, the massive hand and finger 

 themselves forming a tightly fitting and 

 efficient door, and sometimes a very 

 handsome one. In Paiiunis nranuhitus, 

 the great West Indian hermit, the granu- 

 lation to which the specific name is due 

 gives the large claws an appearance 

 of being closely studded with jewels. 

 The next two pairs of legs, which 

 slender, enable these animals to walk 



Male on 



are long and 



with agility, with their houses on their backs, not only 



Pag/lrus arrosor (Herbst). From SarignT, 



under water, where the weight would be less appreciable, 

 but in the open air on the sea-shore, and in the case of 

 some species to great heights and distances inland. In 



