THE RESTING HABIT OF INSECTS, ETC. 5 



temperature, be it high or low, they spin a silken pad, insert the hooks 

 of their prolegs therein, and though surrounded by an abundance of 

 food, remain motionless and torpid alike through the hottest September 

 and the coldest January. Cold here can hardly be the external force 

 or stimulus which acts on the larvfe and produces the reaction of 

 hybernation. Want of food cannot be the cause, for the larva, maybe 

 for the first two or three months of its hybernation, is surrounded with 

 food. Further than that, the same larva will always hybernate in the 

 same skin ; if, as occasionally happens, any deviation from this rule 

 occur, the larva will produce an imago under favourable conditions 

 during the autumn, or will die in the attempt. No amount of applied 

 cold will stimiilate the larva so that it will bring about the reaction of 

 hybernation once this barrier has been passed. 



Are cold and heat, then, the stimuli which, acting on the peculiar 

 organisation of our hybernating or festivating animals, cause the 

 reaction of hybernation and aestivation ? I scarcely think so. At any 

 rate, there can be no doubt that the peculiar forms of torpidity known 

 as hybernation and {estivation are induced in very many instances as a 

 reaction to a stimulus which cannot possibly be either heat or cold. 



Although it is quite possible that the failure of the food supply, due 

 itself to the influence of cold, was, in the first instance, the prevailing 

 factor in hybernation, and that natural selection perfected the various 

 species in that stagein which they were best able to withstand the climatic 

 extremes and the absence of food, yet it is very evident that that is not 

 the whole reason now why certain insects hybernate. As I have shown, 

 some insects, both in the larval and imaginal states, do now in some 

 cases hybernate, in spite of an abundance of food, or anything like an 

 extreme condition of temperature to explain the habit ; neither is it 

 sufficient to say that it is a habit engendered through long ages by 

 natural selection, -without attempting to point out the motive force that 

 causes an insect surrounded by an abundance of food, and by a tem- 

 perature so far favourable to its continued existence, as proved by the 

 fact that many of the specimens of almost every brood do go through 

 their metamorphoses rapidly and successfully whilst their brothers and 

 sisters are in a lethargic condition, to sleep through the long summer 

 and autumn without stir or motion. 



Let us return to a priori considerations again, and look at the 

 matter from another standpoint. 



It would appear that just as the chemical affinities of carbon 

 and some other elements admit of the formation of the com- 

 pounds called organic, and as these possess the capacity, under 

 conditions that we have yet failed to learn, of reacting on one another 

 so as to produce the manifestations that we call life, so all (or nearly 

 all) living matter possessas the capacity of assuming a resting state. 



Probably we know nothing of the very earliest forms of life, but 

 some of those that appear to be the most primitive amongst those we 

 do know, appear, on the approach of drought (being aquatic), to encyst 

 themselves, so as to resist dessication, and, on being moistened again, 

 they either wake up unchanged or break up into parts, each part becoming 

 a complete animal. Nevertheless, all the forms in which we observe 

 this may be, after all, the present stage of an evohition that has gone 

 on through many ages. The rotifers, for example, are so highly 

 organised that they must have a long and varied ancestry. This 



