114 A HISTORY OF RECENT CRUSTACEA 



which belong to Great Britain and are also extensively dis- 

 tributed in the North Atlantic. These are Ilyas araneus 

 (Linn.) and Ilyas coarctatus, Leach. In a tiny specimen 

 of the latter species, taken from off the carapace of the 

 mother, small spines or tubercles are observable on both 

 sides of each of the two divisions of the rostrum, on the 

 outer side of the second antenna?, and on the eye-stalks. 

 These minute characters do not reappear in the adult. 

 The two species mentioned are very abundant on the coast 

 of Sweden, and Aurivillius found that they were almost 

 without exception dressed up either in pieces of different 

 algas (almost always Florideas) or of shallow-water sponges, 

 or with Hydroids, tubicolous Annelids, Polyzoa, Cirri- 

 pedes, or Ascidians simple or compound. His experiments 

 showed him that, if some of these settled rather by the 

 crab's permission than its active interference, yet they had 

 been originally under its control, while in most cases the 

 colonists had been actually planted and forced at the will 

 of the crustacean to occupy their several stations. He 

 found, just as Mr. David Robertson of Cumbrae had done, 

 that his specimens of Hyas were capable not only of dress- 

 ing but of undressing themselves. Of the effectiveness of 

 their disguises he had often had practical experience, when 

 upon visiting his aquarium in the morning he was unablo 

 to find specimens which he had placed thei*e overnight, 

 and which he at first thought must have escaped. Close 

 inspection and the help of a magnifying glass, however, 

 would always show that they were present, but that they 

 had so decked themselves out with the vegetables and 

 animals around them as to lose all invidious prominence. 

 By transplanting into an environment of sponges some 

 that had clothed themselves in bright-coloured algas, he 

 ascertained how accurately they knew their business, for 

 they laboriously picked off the gay colours, and stuck 

 themselves over with fragments of sponge in their place. 



The chelipeds of these crabs are adapted by length and 

 by the flexibility of the joints to reach to the different parts 

 of the body which require dressing up. The hooks and 

 hairs which hold on the tags and patches have been already 



