BODILY CHARACTERISTICS INCONSPICUOUSNESS 287 



remarks: " The caterpillar, chrysalis, and moth of the Black 

 Arches (Psilura monacha] are beautifully protected in this way. 

 The black pupa is fixed in a chink in the bark by a few incon- 

 spicuous threads; its dark colour harmonizes with the shadow in 

 the chink, while the long tufts of greyish hair project and exactly 

 resemble the appearance of lichen. Both larva and moth are 

 coloured so as to resemble common appearances presented by 



Fig. 477. A Beetle (Lithinus nigrocristatus} which resembles Lichen 



lichens, and both habitually rest on lichen-covered bark." Some 

 beetles exemplify the same device (fig. 477). 



MASKING. General protective resemblance to surroundings is 

 effected in a number of animals belonging to widely -different 

 groups by the presence on the surface of their bodies of plant- 

 growths or various foreign substances. Some small West Indian 

 Land- Snails, for instance, escape observation by reason of the dirt 

 with which their shells are covered, but among molluscs a much 

 more remarkable case is that of certain Sea -Snails (species of 

 Xenophorus) (fig. 478). Speaking of one of these, Chun (in Aus 

 den Tie/en des Weltmeeres] describes it as "a snail which pos- 

 sesses the remarkable habit of cementing to its shell in a sym- 

 metrical manner the empty shells of other snails. It might almost 

 be imagined that an artistic hand took part in grouping these 

 foreign shells." Bits of coral and stone may also be included. 



Even more remarkable devices are adopted by some of the 

 Crustacea. There are, for example, various kinds of Spider-Crab 

 (species of Maia, luachus, Stenorhynchus, &c.) in which the body 

 is covered with a thick growth of sea- weed, and it has been shown 

 by Bateson and others that this is not an accident, for these 



