THE RESTING HABIT OF INSECTS, ETC. 55 



protests, however, that it is not sufficient to refer these phenomena to 

 the operation of ancestral habit, brought about by this agency, " with- 

 out attempting to point out the motive force that causes an insect, 

 surrounded by an abundance of food, and by a temperature so far 

 favourable to its continued existence ... to sleep through the 

 long summer and autumn without stir or motion." In reply, I would 

 venture to express my opinion that this and similar anomalous habits 

 is one of the unreasonable survivals of once suitable adaptations. 

 It may be that at the period when the climate of such part of Europe 

 as was inhabited by Arctia caia, Vanessa urticae, V. io, and Gonep- 

 teryx rhainni, approximated to that now obtaining in North Scan- 

 dinavia, with a very short summer and long winter, all these insects 

 acquired a habit of lengthened hybernation. But during the succeeding 

 ages the idiosyncrasy of the former two may have enabled them par- 

 tially to conform to their more favourable environment, so that they 

 have in part emancipated themselves from the periodicity of the habit, 

 while the latter two have uniformly retained it ; so that every indi- 

 vidual hybernates so soon as they have sufficiently replenished them- 

 selves with food as to attain fully nourished conditions. The case of 

 Spilosonia nienthastri may be that its larva was capable of attaining 

 its full development from ovum to pupa exactly within the summer 

 limit, and so never acquired the power of hybernating as a larva ; 

 while its relative, Arctia caia, in its development either did not syn- 

 chronise so well, or was less conservative in its habits, and bred 

 rapidly and continuously Avhen altered conditions favoured it. But 

 the changes and chances undergone in primaeval epochs by European 

 Lepidoptera, a large proportion of which are thought to have immi- 

 grated from Siberia, '•■' have been so mutable and various, that we can 

 only guess at the alchemy by which nature evolved the vital phe- 

 nomena now exhibited. No more interesting study could be imagined 

 than to trace the behaviour of various species of the same genera 

 under natural conditions in different climates. The result of such 

 researches might give us some sure footing Avhen venturing upon the 

 uncertain morass of speculation. Some such line of enquiry, I pre- 

 sume, was intended by the rather enigmatical remark, " It would be 

 interesting to examine the internal forces which were acted upon, and 

 which responded in so large a manner to the outside stimuli as to 

 ensure success." 



Some butterflies and moths, as has been already stated, are pecu- 

 liarly capable of adaptation, and some therefore have a very extensive 

 geographical range. Vanessa levana, which is said at its extreme 

 N. Russian limit (60*^ to GS*^) to have but one annual brood (the type), 

 has as many as three in Southern Europe. Dinuthoecia capsophila 

 emerges indiscriminately from the end of April till the middle of 

 August, and hybernates both in the pupal and occasionally in the 

 larval stages. The larvae of butterflies in the arctic regions are 

 believed to hybernate twice before completing the cycle of metamor- 

 phoses. Certain of our own Lepidoptera are only double-brooded in 

 the warmer portions of the British Islands. May we not conjecture 

 that in the intermediate zone such a species might occasionally attempt 

 to reproduce itself twice, with possibly either of two results, namely, 

 that by natural selection a race would survive capable of hybernating 

 as a larva, while the southern race would retain the pupal hyljernation ; 



* An article on the grounds that form the basis of this supposition would be 

 most interesting from our thoughtful contributor. — Ed. 



