I ^0 -ANIMAL COLORATION. 



brown catkins ; thus a larger number would have a chance of 

 ^scaping the attention of insect-eating birds than if the cater- 

 pillars were all green or brown. 



Variable Protective Resemblance in Chrysalids. 



The chrysalids of most moths which lie in the ground 

 at the foot of the tree upon which the larva has fed 

 <ire brown in colour, and therefore assimilate more or less 

 closely to the colour of the soil. Such pupte are, however, 

 commonly enclosed in a slight cocoon. Probably the immo- 

 bility of the pupa (unless it be touched) has more to do with 

 their escaping enemies than the colour ; the colour is due 

 chiefly to the thickness of the chitinous layer ; this substance 

 (chitin) forms the u shells " of Crustacea and insects, and is 

 transparent when in thin layers ; as the thickness of the chitin 

 is increased, it becomes golden yellow, and finally brown. 

 The resemblance of pupa? to the soil can, therefore, hardly be 

 regarded as an adaptive colour ; fortunately for the insects 

 it happens that the colour of the pupa coincides with that of 

 the usual environment. If there has been adaptation any- 

 where in this case, it is probably in the assumption of the 

 habit of pupating underground. Many insects, however, par- 

 ticularly butterflies, form themselves into a chrysalis in an 

 exposed situation ; in these cases the chrysalis is either naked 

 or wrapped in a cocoon formed by the caterpillar. Sometimes, 

 as in the case of the Puss Moth, particles of the surrounding 

 surface are woven into the cocoon, which in this way very 

 perfectly protects the enclosed chrysalis.* 



The pupa3 of butterflies which have no cocoon possess a 

 remarkable power of adapting themselves to the hue of the 



In this particular case the cocoon is not only like the trunk of the 

 tree against which it is placed, and from fragments of which it is con- 

 structed, but exceedingly, hard : this is, of course, an additional protection. 



