MIMICRY. 587 



contrary, an important means of protection. The Crabs in 

 question escape pursuit in consequence of this disguise, and it is 

 to be observed that each species chooses the very material which 

 makes it most unrecognizable to plant upon the exterior of its 

 body; those species which live chieflvin regions where Cystosiras 

 are indigenous deck themselves in Cystosiras, whilst those which 

 inhabit the same places as Ulvce carry Ulvce on their backs.* 

 This also serves as aggressive mimicry ; for, as Mr. Woodward 

 writes, " thus disguised like Indians stalking game, they can 

 readily approach their more active prey."f Mr. Bateson observed 

 this active mimicry at Plymouth, and describes how a Crab 

 seizes a piece of weed, tears off a fragment, chews the end in its 

 mouth, and then rubs it firmly on its head and legs until it is 

 caught by the curved hairs and fixed. " The whole proceeding 

 is most human and purposeful. Many substances, as Hydroids, 

 Sponges, Polyzoa, and weeds of many kinds and colours, are 

 thus used ; but these various substances are nearly always sym- 

 metrically placed in corresponding parts of the body, and par- 

 ticularly long plume-like pieces are fixed on the head."t Dr. 

 Willey records a similar observation which he made on the faces 

 of rocks near Tjibodas (Java). " I found a quantity of small 

 caterpillars living on the powdery Alga which makes greenish- 

 white patches on the rocks. The caterpillars had so completely 

 covered themselves with the Alga as to be only discernible by 

 their movements on close inspection, and their disguise must 

 effectually protect them from foes."§ " Equally marvellous, too, 

 is the case of many kinds of caterpillars which spin their cocoons 

 on the bark of trees, and cover the structures wherein they are 

 subsequently to undergo transformation into the chrysalis state 

 with lichens and fragments of bark, that their temporary resting 

 place may not be noticed by insectivorous birds." || When the 

 caterpillar of the Indian butterfly, Limenitis procris, " comes out 

 of the egg, it betakes itself at once to the very point of a tender 

 leaf, and eats down steadily on both sides of the midrib, which 



* Kerner and Oliver, ' Nat. Hist. Plants,' vol. i. p. 77. 



j ' Cassell's Nat. Hist.' vol. vi. p. 197. 



{ Cf. J. A. Thomson, ' Study of Animal Life,' 2nd edit. p. 62. 



§ ' Natural Science,' vol. vi. p. 407. 



|| Kerner and Oliver, ' Nat. Hist. Plants,' vol, ii. p. 159. 



