150 THE BOOK OF NATURE STUDY 



must be a difficulty. Again, in some localities, shells are difficult 

 to obtain, and the hermits are obliged to resort to all sorts of 

 devices they may be found in hollow cabbage stalks, in mere 

 broken fragments of shell and so on. 



Hermits are not very easy to keep alive in captivity, perhaps 

 because the borrowed shell makes respiration difficult, at any 

 rate the first symptom of malaise that they show is an insane 

 desire to move from one shell to another, even if the new shell 

 is no better than the old. In dying also they always leave the 

 shells. Specimens for the aquarium should be small, and the 

 vessel in which they are placed should not be crowded. Do not 

 attempt to keep more than two or three specimens at once. The 

 habits are interesting. Note that one claw is bigger than the 

 other so as to fit the animal to its borrowed shell, note also the 

 long antennae, the sudden recoil into the shell on the approach 

 of danger, the reduction of the functional walking legs to two 

 pairs, and the very mobile stalked eyes. Large specimens, in- 

 habiting big shells, have sometimes in the shell with them a 

 large worm, which is not a parasite, for it does the hermit no harm 

 beyond taking perhaps a share of its food, but merely a messmate, 

 seeking shelter from its enemies in the hermit's roomy house. 



The above contains some mention of the more important 

 types of the higher Crustacea, but there are various simpler 



forms of which a few words 

 may be said. As a general 

 rule, the shrimps and prawns 

 are not easy to keep alive 

 in captivity, but the attempt 

 should be made, if only to 

 give an opportunity of study- 

 ing their structure. The 

 common shrimp is interest- 

 ing because of its close re- 



FiG.72.-A common prawn (Palcemon sguilla}. semblance m colour to the 



sand in which it lives. As everyone knows, boiling changes 

 the sandy tint into a reddish-brown colour. Very interesting also 

 is the shrimp's method of burying itself. It first makes an ex- 

 cavation by rapid movements of its legs, and then completes the 



