294 ANIMAL DEFENCES 



half were dark-brown, though about one or two per cent took their 

 colour from the leaves present. Adaptability to surroundings as 

 regards appearance is exemplified not only by caterpillars but also 

 by the chrysalides of some moths and butterflies. No better 

 example could be selected than ;he Small Tortoise-shell Butterfly 

 ( Vaiiessa tirticcB), upon which Poulton conducted a remarkable 

 series of experiments. By varying the surroundings at the time 

 when the caterpillars become quiescent preparatory to passing 

 into the motionless pupa-stage, he was able to produce at pleasure 

 dark, light, and gold-coloured chrysalides. The utility of a gilded 

 appearance is not at first sight obvious, but it may be pointed 

 out that it would harmonize with a rock-surface which presented 

 such glittering minerals as mica (flakes of which are used on 

 Christmas trees and the like to give the glistening appearance of 

 snow). Rock-surfaces in our damp climate are generally dull, 

 except when freshly fractured, but in hotter and drier countries 

 they often present a glittering appearance, and in this connection 

 it is interesting to note that the word chrysalis, which means 

 golden (Gk. chrysos, golden), is taken from Aristotle, and was 

 no doubt given from the appearance of certain pupae noticed by 

 the ancient Greeks. Possibly, therefore, the power of producing 

 gilded chrysalides possessed by the caterpillars under discussion 

 may be reminiscent of a time when the ancestors of the Small 

 Tortoise-shell Butterfly inhabited more southern latitudes than 

 ours. The range of this particular species at the present time 

 includes a good deal of the northern hemisphere, and the distri- 

 bution of the family to which it belongs (Nymphalidse) is world- 

 wide, so that there is nothing improbable about the suggestion. 



SPECIAL PROTECTIVE RESEMBLANCE 



Here are included cases where inconspicuousness results 

 from resemblance to some special inedible object, instead of 

 being due to properties of form and colour whereby harmony 

 with the general surroundings is brought about. There is, how- 

 ever, no sharp boundary-line between these cases; e.g. a brown 

 yEsop Prawn may not only assimilate generally to the appearance 

 of the weed to which it clings, but may also simulate a special 

 part of this. Special Protective Resemblance, like the other form 

 of assimilation, may be either constant or variable. 



