THE KNTOMOLOGIST S RECORD. 



appear to have a causal connexion. Cold and hybernation appear to 

 be such, but what proof is there of the causal connection ? 



If cold be the external stimulus which, actinj^ on the peculiar 

 organisation of Pyrameis atalanta, and on such moths as Gonoptera 

 lihatrix, Orrhodia vaccinii, Xi/liiui socia, Scopelosoma satellitia, 

 Hoporina croceago, Dasijcampa ruhi(jinea, Cidaria miata, Hijpena 

 rostra}is,Pterophorusmonodactylus,iindnVcinyH]}eciesoiDesp)-essariae, 

 causes them to go into hybernation on the advent of low temperature, is 

 cold to be considered the external stimulus which produces the reaction 

 of hybernation in Gonepteryx rhamni and Vanessa io, which go into 

 hybernation at a comparatively early and comparatively warm season 

 of the year ? If you answer yes, cold is still the stimulus, but the 

 amount of cold necessary to produce the reaction in the organisation 

 of these insects is less than that required in the previous cases, what is 

 to be said of those specimens of Vanessa urticae, Avhich go into 

 hybernation in the summer months, and remain torpid from June until 

 March — that is throughout both the hottest and coldest periods of the 

 year ? If you say that the hybernation of this species ought rather to 

 be considered {estivation, and that heat is possibly the external in- 

 fluence, I would answer that in those seasons in which three broods 

 emerge in a year, in June, August and October, a certain percentage of 

 each brood goes at once into hybernation, and if we accept the fact that 

 heat is the stimulus which drives the June and August specimens into 

 hybernation, is cold the stimulus which produces the reaction which 

 throws the October specimens into a torpid condition ? We may agree 

 with the learned Professor that "we are unable to demonstrate with 

 the microscope the fine ' molecular ' or histological variations in the 

 nervous and other systems on which the capacity for hybernation may 

 depend," we may further agree that " such modifications must exist, 

 and that they cannot be regarded as a direct effect of the cold, but must 

 rather be looked upon as arrangements to counteract its influence," 

 but having granted all this, we would ask again. Is the learned 

 Professor at all sure, what evidence has he that cold is the external 

 influence which directly induces hybernation in very many instances ? 

 I would meet this difliculty by suggesting that the failure of the food 

 supply was the external stimulus which brought about the reaction, but 

 this is open to almost the same objection as cold. True, the failure of the 

 food supply runs side by side with the phenomenon of hybernation, and 

 appears to oft'er a more closely causal connection even than cold. The 

 moths and Fyrameis atalanta do not go into hybernation until the ivy 

 nectar fails ; Vanessa io and Gonepteryx rhamni do not (perhaps can- 

 not) take the ivy sweets for food, and so they disappear when clover 

 and wayside flowers fail to yield sufficient stores. But Vanessa urticae 

 again laughs and defies such a connection. It takes on a torpid con- 

 dition when there is an abiuidanco of food, and renuiins torpid during 

 a period in which its own brothers and sisters maybe are imbibing 

 their fill. 



The hybernation of caterpillars, too, throws some interesting light on 

 the subject. Our tree-feeding kinds which hybernate small, such as those 

 of Lasiocampa quercifolia, Bomhyx quercus, Apatura iris, Limenitis 

 aybilla, and dozens of others, always hybernate snuill. Hatching as 

 early as June, July or August, with an abundance of food everywhere 

 around them, they feed up to a certain size, and then, whatever the 



