236 THE WONDER OF LIFE 



and trim it. Some crabs use the tests of sea-squirts or 

 pieces of sponge and zoophyte. In a number of higher 

 crustaceans (crabs, lobsters, etc.), a sahvated cement of 

 saud is plastered over the carapace, making it very like 

 the substratum. In species of the somewhat primitive 

 type known as Dorippe, the posterior hmbs are turned 

 upwards and they hold the disguise — which may be almost 

 anything, even a piece of glass — in position over the back. 

 Most remarkable are the cases where crabs take seaweed 

 of the colour that suits their usual background. 



The process of masking in one of the spider-crabs {Maja) 

 has been very carefully studied by Minkiewiez. The crab 

 seizes a piece of seaweed in its forceps, puts it into its 

 mouth and cuts off a piece, and then fixes this by means of 

 its forceps on the back or on the walking legs. It moves the 

 forceps backwards and forwards till the alga fixes on some 

 of the recurved and barbed hooks borne on the carapace 

 or legs. The same is done with sponge, hydroid and com- 

 pound Ascidian, and Minkiewiez got his crabs to dress 

 themselves up in pieces of silk paper. Professor Fol 

 once made a similar experiment, giving the crab pieces of 

 hay and white paper and depriving them of seaweeds. 

 Unsatisfactory as the dress material was, it was duly 

 utilized. 



Minkiewiez made the interesting experiment of placing 

 two or three thoroughly cleaned crabs in an aquarium 

 and giving them pieces of silk paper of two colours — 

 one the same as the environment and the other different, 

 with the result that the crabs chose the pieces with the same 

 colour as the surroundings. ' If the walls are white, they 

 will be covered with white only ; they will take neither 

 green, nor yellow, nor black ; if the walls are green, they 



