216 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



Hyas araneus, Lin. 



[Read 27th December, 1887.] 



This crab is not uncommon in the Firth of Clyde 

 from low -water to 20 or 30 fathoms, mostly on a 

 hard or gravelly bottom, and generally covered more 

 or less with sea-weed and other organisms. There 

 is a common belief that these organisms get attached 

 to the crab by chance — a view favoured by the fact 

 that the plants appear on the animal in their 

 natural position ; — and when we consider the multi- 

 tude of spores floating in the sea and settling down 

 to grow where they find suitable conditions for their 

 development, it is plausible enough to think that 

 the crabs may get their false covering in that way. 

 There can, however, be no doubt that several of the 

 crab family attach foreign matter to their carapace 

 and limbs, and there seems to be as little doubt that 

 this is done for a means of concealment from their 

 enemies ; but whether all the foreign matter found 

 on the crabs is so placed through the intelligence 

 of the animals cannot so certainly be determined. 

 Balani and Serpnlcv are often the prevailing ex- 

 traneous organisms, especially on Hyas araneus, but 

 we cannot well believe that they were placed there 

 by the crab, as they cannot (if we may use the 

 term) be transplanted ; yet, as we shall see, the crab 

 can, with its flexible limbs, pluck the weeds off all 

 parts of its body, and it might therefore arrest the 

 growth of the parasites if so inclined. It is accordingly 

 just possible that these parasites may be tolerated 

 by the crab from useful motives, viz., that they may 

 settle down and grow, and so afford a means of 

 protection similar to that secured by animals which 

 assume the colour of the plants among which they 

 harbour— e.g., Hippolyte varians, Leach, that is found 

 green among green Zostera and brown among brow n 

 Halidrys. As these Balani and Serpulir are chiefly 

 on the crab when located on hard or stony ground, 

 it will in this garb simulate the stones and gravel 

 among which it lurks, and possess a means of con- 



