338 



ANIMAL DEFENCES 



an extremely thick carapace, strengthened by the deposit of 

 lime-salts, and the insignificant tail which, if left sticking out, 

 would constitute a weak place in the defences, is kept tucked 

 up out of harm's way into a depression on the under surface. 

 The walking-legs, too, can be folded up under the body, and 

 the great pincers brought together in front. The Northern 

 Stone-Crab [Lithodes maid) (fig. 498), pleasingly termed the 



Fig. 498. — The Northern Stone-Crab {^Lithodes maza), reduced 



Devil-Crab by the Norwegians, and allied species from Japan 

 and elsewhere, are so thickly covered with sharp spines, pincers, 

 walking-legs and all, that they would undoubtedly prove rather 

 trying mouthfuls to even the most sharp-set of enemies. The 

 front part of the body of the Rock- Lobster {Palimiriis) (see vol. i, 

 p. 412) is also pretty well off in the matter of spines, though at 

 first sight it seems odd that its large tail should be quite smooth, 

 while part of the tail-fin is soft. The seeming anomaly is cleared 

 up when we remember that this animal is in the habit of watching 

 for prey with the smooth tail sheltered in a crevice, so that only 

 the thorny part of the body is exposed to the attacks of more 

 powerful creatures. Accommodation of armour to growth is 

 effected in this group by a method differing entirely from the 

 economical Molluscan plan. A Crustacean, in fact, undergoes a 

 series of "moults" until the adult maximum size is reached, and 

 these are very frequent in early life. At such times the entire 

 hard covering of the body is cast off, and also the firm lining of 

 the stomach (see vol. i, p. 407). 



In free-living Brisde- Worms {Chcstopodd) the bristles may be 



