122 The Irish Naturalist. [May, 



the water if need be. It is said that Polybius even pursues 

 active fish like the mackerel, and fastening on to one by its 

 sharp and powerful pincers, holds tight until its victim is 

 exhausted. 



Another group of curious, and in some cases quite weird- 

 looking crabs, is that containing the s^^ider-crabs. These 

 forms, as their name sufficiently denotes, possess long spidery 

 legs, wdth comparatively small bodies, which latter in this 

 case, are triangle-shaped, with the point directed forwards. 

 Notwithstanding all their long limbs however, they are 

 sluggivSh, slow-moving animals, and in consequence readily 

 fall a prey to fishes and other enemies. Nature, which gene- 

 rally devises some plan for the protection of slow-moving or 

 awkward forms, has here accomplished that purpose in a very 

 interesting way. For years before the true nature of the case 

 was understood, these crabs had specially attracted the 

 attention of observers, from their very untidy appearance. 

 Their shells were generally more or less overgrown by sea- 

 weeds or various kinds of fixed and colonial animals. 

 Fortunately some of these forms have been kept in captivity 

 of recent years, so that their habits have been definitely 

 observed. The crab known as Hyas, which has not really 

 such very long legs, but evidentl}^ belongs to this group, is 

 usually so overgrown by colonies of sea-mats, etc., that its 

 true form is entirely hidden, and one can well believe that it 

 would be well-nigh indistinguishable in its native wilds. But 

 although these organisms are growing happily on the crab's 

 shell, the3^ did not settle there of themselves, as one might 

 perhaps suppose. It has in fact been observed that these 

 crabs, if placed quite clean in an aquarium with sea-weeds and 

 living sea-mats, will actually tear off little bits of them, and 

 deliberately plant them on the back of the shell ! By their 

 marvellous, instinct too, the crabs know well enough what 

 organisms will bear this rather rough-and-ready transplanting, 

 for the pieces they plant are always such as will live and grow. 

 All the observers who have had these interesting creatures 

 under their notice, remark on the effectiveness of the disguise, 

 and in fact there have been cases in which the crab was at 

 first thought to have escaped, from the way in which it had 

 entirely disappeared. 



