298 THE CAUSES WHICH 



moss or lichen, green or faded leaf, dropping of birds, and that 

 general tone of reproductive beauty which varies in fervour as the 

 climatic zones of the globe, acquire for them photographic con- 

 cealment in their haunts, and here they hide from their enemies, 

 a juncture at which Nature now and again steps in, exerting a 

 gradual influence, selecting and perpetuating such races even to 

 the elimination of an original type. Other insects, again, 

 which retain in a locality their conspicuous colours, are either- 

 distasteful to the greater part of the birds that there resort by 

 possessing weapons of defence or obnoxious secretion, or are those 

 Nature has shielded by giving protective resemblance to such 

 species or to surrounding inanimate objects. Neotropical butter- 

 flies thus mimic the acrid kinds [Heliconidce), and many indi- 

 genous flies are scarcely distinguishable from stinging bees on 

 the umbels of flowers, while moths, beetles, and bugs resemble 

 them in form and actions. It is, then, evident, were change 

 induced in natural surroundings, soils, light, vegetation, &c., 

 that thus afford protection to groups of insects, a certain portion 

 would be destroyed, and a new era of protective selection induced. 

 Messrs. Buckler, Hellens, Porrit, and others have recently given 

 considerable attention to the breeding of our indigenous Lepidop- 

 tera, and a perusal of their life histories I think will allow us to 

 gather, firstly, that a change of appearance in the larval state is 

 not in direct relation to variation of the imago, since the typical 

 caterpillar often produces a variety and the larval aberration a 

 typical butterfly or moth ; and, secondly, that certain laws regu- 

 late variation in caterpillars. For example, the differentiation is 

 generally effected by chromatic change through a scale of yellow, 

 green, grey, pink, and brown, or by obliteration of the longitudinal 

 and transverse markings. Thus the larvae of the Holly Blue vary 

 from yellowish-green to green and black, or the extreme segment 

 is sometimes pinkish ; those of the Spurge Hawk from bronze- 

 green to blackish bronze ; those of the Death's Head from green 

 to olive brown ; those of Noctiia umhrosa from yellowish to 

 greyish brown ; those of the geometer Ej)h}/ra punctaria from, 

 green to pinkish brown ; or those of E. pendularia from pinkish 

 purple to bright green ; those of the Yellow Shell Moth from 

 greenish grey to pinkish grey and pinkish brown. The " Wave " 

 Acidalia degeneria again has larvae blackish brown, marked with 



