16 BRITISH LEPIDOPTEEA. 



what are here called Normals, i.e., the form which is especially well 

 clothed in the fifth instar in which the larvae hybernate, nevertheless 

 both Forward and Laggard forms do occur not uncommonly, and 

 probably many of the various intermediate forms, some of which are 

 above described. 



The fact that, out of a single brood treated identically, some should 

 require but six stadia, and others fourteen, to reach maturity, and this, 

 as a simple matter of variation and not of disease, is remarkable. 

 One is tempted at once to ask what is the use to the species of this 

 variation, and Chapman suggests that since the Forwards are decidedly 

 favoured, if not caused, by a high temperature, it appears that if, in a 

 warm and early season, only the Normal form existed, these would be 

 ready to hybernate at midsummer, and would probably largely perish 

 in consequence, whilst the larvae from a second brood of Forward 

 moths would in such a season, reach the hybernating stage at a fairly 

 favourable date. In an early English summer the Forwards them- 

 selves, or their progeny, would no doubt perish, hence possibly the 

 rarity of wild Forwards in England. It is obvious that the large 

 hybernating form (No. 3 ante), with its larger store of nutriment and 

 denser clothing, appears to be specially adapted to carry the species 

 through a long and severe winter. The Laggards, on the other hand, 

 appear to be particularly suitable to a mild winter, in which hybernation 

 is impossible, though a little feeding could be done, but no real progress 

 made. These different forms obviously exist commingled in our 

 English race of A. caia, the Normals largely predominating, but ready 

 to give way to the Forwards under the influence of a high temperature. 

 Chapman's conclusions from his experiments on Arctia caia are 

 stated as follows: — " (1) The larva of A. caia possesses three types, 

 each with subsidiary varieties. (2) Each of these types, and, indeed, 

 each subsidiary variety, is characterised by a series of moults, a suc- 

 cession of plumage, and habits as to hybernation, in which it differs 

 from the others. (3) A. caia, as we meet with it, may be regarded as 

 a mongrel race, consisting of these three types, closely mixed and 

 intercrossed, but capable of separation by appropriate breeding and 

 selection, or more probably of two races, one with hybernating larvae 

 and a single brood annually, the other of an alternating summer and 

 winter form. (4) Though these two races may conceivably, under 

 certain climatic conditions, have existed as separate and pure races 

 (and may do so now in some parts of the world), yet the hybernating 

 form is most largely represented, at present, in England, with a small 

 intermixture of the digoneutic form, which persists, as it enables the 

 species to be continued in exceptional seasons that would be destruc- 

 tive to the dominant monogeneutic type." 



The changes that almost all larvae undergo at each stadium are 

 such that they often give important clues to the phylogeny of the 

 species. No doubt, in the case of many (? all) species, the modifi- 

 cation observed at each successive instar, bears a fixed relationship 

 to the habits of the larva during that instar, and it is noticeable that 

 larvae that hide by day, or obtain their meed of protection by their 

 similarity to their immediate surroundings, e.g., larvae of Noctuids, 

 Geometrids, or those that are internal feeders, vary least in their 

 superficial appearance at each instar. Generally speaking, those larvae 

 that are most modified in appearance at the various moults, lead a 



