ON THE LARVA OF ARCTIA CAIA. 289 



The great mass follow the habit I have just described as the normal 

 one, becoming moths nearly 12 months after the eggs are laid ; whilst 

 there are usually a very few, sometimes none, that progress very slowly 

 and moult a number of times ]>efore assuming fuli(j/nosa or caia 

 plumage. 



In each of these groups there are several subsidiary varieties, and 

 there are even groups that appear doubtful as to which of these lines 

 they are following. 



For convenience in my notes I have called these three forms the 

 Forward, the Normal and the Laggard types, and the names, if not 

 elegant, are at least expressive. 



Having met with these types and some subsidiary ones in my 

 original brood of caia, I proposed to continue rearing them pedigree 

 fashion, with a view to discovering how far each of these forms was 

 hereditary and what circumstances determined the appearance of each 

 form. Limitations of time and s^jace led me, however, to follow only 

 the Forward group, chiefly because it Avas the most easy to do. 

 Of these several broods could be raised in a year, Avhilst of the 

 others, besides the difliculties attendant on hybernation, only one brood 

 a year was available. My observations were made, therefore, on six or 

 seven consecutive broods (generations) of the Forward type — that is, 

 the Forward specimens in each brood were used as the parents of the 

 next brood observed, though I also bred several broods from Normal 

 liybernating larvae, both after hybernation and after forcing. 



The presumption, of course, is (and my observations, so far as they 

 went, confirm it) that, so far as the points to which I directed my 

 attention are concerned, pedigree Ijreeding of the Normal ty2)e will 

 iilways produce just such a brood as may be obtained from eggs laid by 

 a wild moth. Still one would supjjose that there is, in the wild state, 

 occasional crossing both of Forwards and Laggards with the Normal 

 form, and prolonged pedigree breeding of the Normal form to the 

 elimination of the others might produce some interesting results. I 

 fear no one is likely to take this up for its own sake, as the labour and 

 patience required are much in excess of the a^jparent value of the 

 result ; but some one, with the perhaps more attractive object of 

 raising varieties of the imago of caia, would find it add little to his 

 trouble and much to the value of his results, if he combined therewith 

 pedigree breeding of Normal (larvjx} of) caia. 



Pedigree breeding of Laggards would be even more tedious, and 

 jjrobably also more difficult, but might be expected to present many 

 interesting points. I hardly tried to follow this up, and did not succeed 

 at all. 



The Forward gi'oup of larvae that I more particularl}- followed out, 

 are, or perhaps appear to be (because I did follow them out and 

 think I understand them) the simplest in their subsidiary varieties and 

 in tlie circumstances governing the assumption of this form rather than 

 of the others. 



It appears to be entirely a matter of temperature ; my broods were 

 reared at a temperature rarely far from 60°-65°, and after six generations 

 continually raised from Forwards, the projoortion of this form remained 

 at about 5 per cent, of the larvae raised. In this number of generations, 

 selection had j^i'oduced no effect whatever in the direction of securing 

 a form consisting entirely of Forwards. 



