ON 1?afc LARVA 0^ ARCl*IA CAIA. 131 



"With special reference to its correlated variations in Plumage, 

 Moulting and Hybernation. 



By T. A. CHAPMAN, M. D. 



{Continued from page 35). 



In considering the relations which these variations in plumage, 

 moulting and hybernation bear to one another and to the history and 

 habits of the species, some very interesting conclusions present them- 

 selves, not indeed as proved, but as highly probable. 



In the first place, it is very interesting to find that of a single l)rood 

 of larvEe treated identically, some should reach maturity in five moults, 

 whilst others take thirteen, and this as a matter of simple variation, and 

 quite apart from any disease. Such a gi-eat range of variation may, 

 probably does, exist in other hybernating Arctiae, but in no other hyber- 

 nating larvae, that I have reared or heard of, is it met with. Mr. 

 Hellins records frequent and continuous moulting in some few instances, 

 but these were always, in his opinion, pathological. 



As to the use of these variations to the species ; we find in the first 

 place that the Forward forms are decidedly favoured, if not caused, by 

 a high temperature. Now, if only the Normal form existed, it is 

 evident that in a very warm and early season these would be ready to 

 hybernate at midsummer, and would jDrobably largely, if not entirely, 

 perish in consequence ; whilst a second brood from the Forward moths 

 would reach the hybernating stage at a fairly favoiirable date. In an 

 ordinary English summer, no doubt the Forwards themselves or their 

 jirogeny Avould perish ; hence, no doubt also, the rarity of Forwards in 

 England. It is olivious again, that the fine large hybernating form of 

 larva, noted as appearing in Brood I, from its larger store of nutriment, 

 its denser clothing, and greater resistance to change of temperature, was 

 well adapted for carrying the species through a long and severe winter, 

 that might be fatal to the ordinary hybernating form. 



Then the Laggards may be supposed to take up precisely the opposite 

 role, and to be suitable to a very mild winter, in which hybernating 

 would be very difficult, although feeding up would be impossible. 



These four forms obviously exist, freely commingled in our English, 

 race of caia, but with the Normals largely predominating, though ready 

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



My experiments amounted to an attempt to produce a race which 

 shoiild be entirely Forwards, but in this, broadly stated in this form, 

 they entirel}'^ failed. They did apjtear, however, to produce a certain 

 effect on the form assumed by the larvfe. They did, most esjiecially, 

 j)roduce an increase of the Laggards, and not only an increase in their 

 numbers, but an increase in their variety, and in their constitutional 

 stamina. I deduced from this, tliat there was a closer relationship be- 

 tween the Forwards and the Laggards, than between either of tliem and 

 the Normals, probably to be explained by the supposition that a warm 

 summer, favouring the production of Forwards, belonged to a climate 

 where the winter was also warm, which would favour Laggards ; so 

 that the existence of a race of caia consisting entirely of Laggards or 

 entirely of Forwards, was extremely unlikely ; one that alternated 

 between Forwards and Laggards was probably not infrequent, and may 



