

THE ARTHROPODS 147 



colour change of Carcinus, but have an even more interesting 

 peculiarity that of actually planting on their backs seaweed 

 or sea-firs. That this is intentional and is done with a desire 

 for concealment i.e. is not a mere accidental growth is readily 

 seen by taking a spider crab from a pool and putting it into a pie- 

 dish containing weed or zoophytes differing in colour from that 

 already on the animal's back. In a very short time it will be 

 seen that the crab has carefully fixed the new weed in place of 

 the old, so that it is no longer conspicuous but resembles its 

 surroundings. The back of the crab is furnished with hooked 

 hairs to which the weed is attached. Spider crabs are sluggish 

 animals, with none of the restless activity of the shore crab. 

 A common form is Hyas araneus, most abundant on the east 

 coast, while on the west the much larger Maia squinado occurs, 

 being especially abundant in Cornwall. We have also a consider- 

 able number of other species. 



The crabs just mentioned show striking distinctions from 

 lobsters and their allies, but we have a series of small but interest- 

 ing forms which are in some respects 

 transitional between the two. Search 

 under stones in muddy pools, turning 

 over those of the stones which have a 

 cavity between them and the mud 

 beneath, and you will probably find 

 specimens of the hairy porcelain crab 

 (Porcellana platycheles) , with its large 

 flattened claws, deeply fringed with Fl \ 7 / I '" Th j ; hai ^ P; c f * in 



crab (Porcellana platy elides}. 



bristles. The carapace is curiously 



rounded, and striking differences from the true crabs are the fact 

 that the antennae or feelers are long, not short, and that there are 

 only three pairs of walking legs behind the great claws, the fourth 

 pair of the true crabs being represented here by a pair of slender 

 rods, generally kept folded beneath the carapace, which end in 

 a brush of hairs. Our other species of porcelain crab (P. longi- 

 cornis) is to be found on the attaching roots of the great oar- 

 weed. Tear up a plant of this from the rocks to which it is fixed, 

 and you will probably find a little reddish crab climbing about 

 the base. It generally resembles the hairy form, but is without 



