BODILY CHARACTERISTICS INCONSPICUOUSNESS 289 



are nearly always placed symmetrically on corresponding parts 

 of the body, and particularly long, plume-like pieces are fixed 

 on the head, sticking up from it " (Bateson). 



Some Sea- Urchins render themselves very inconspicuous by 

 heaping bits of stone and shell upon their bodies. One would 

 be inclined to think their firm spiny shell quite enough by way 

 of protection, but it does not keep off star-fishes. 



The last example of masking to be noted here is that of a 

 large red Sea -Anemone (Tealia crassicornis] which abounds on 

 our coast. The body of this creature is covered by sticky knobs, 

 to which small pieces of stone adhere. When uncovered by the 

 tide the animal draws in its tentacles and shrinks into a rounded 

 lump, which, in virtue of its extraneous covering, looks like a 

 little heap of gravel, and is commonly overlooked by those un- 

 aware of the facts of the case. 



VARIABLE GENERAL RESEMBLANCE 



The examples of protective resemblance so far quoted are 

 mostly permanent adaptations to one particular sort of surround- 

 ing. There are, however, numerous animals which possess the 

 power of adjusting their colour more or less rapidly so as to 

 harmonize with a changing environment. 



COLOUR-CHANGE IN SNOW- ANIMALS. Some of the best-known 

 of these cases are found among those Mammals and Birds which 

 inhabit countries more or less covered with snow during a part 

 of the year. A good instance is afforded by the Irish or Variable 

 Hare {Lepus variabilis\ which in these islands is chiefly found in 

 Ireland and Scotland. In summer this looks very much like an 

 ordinary Hare, though rather greyer in tint and smaller in size, 

 but in winter it becomes white, with the exception of the black 

 tips to the ears. Investigations which have been made on the 

 closely-allied American Hare (Lepus Americanus) seem to show 

 that the phenomenon is partly due to the growth of new hairs of 

 white hue, and partly to a change in colour which affects the tips 

 of the ordinary hairs. In both cases the whiteness would appear 

 to be the result of the presence of minute bubbles of carbonic acid 

 gas in the substance of the hairs themselves, they absorbing the 

 gas from their roots, where it would appear to be generated. The 

 Common Stoat (Putorius ermineus] (see figs. 315 and 316) is sub- 

 ject to similar colour -change in the northern parts of its range. 



VOL. II. 51 



