( lxxxviii ) 



Insensitiveness of many organisms. 



And yet we know there are myriads of insect organisms 

 in an immature condition, apparently waiting for nothing but 

 development, which are absolutely insensitive to the influence 

 of a heightened temperature, nay, in some cases, as it were, 

 resent that influence, and are moved by it in the opposite 

 direction, that of delay or postponement. This radical dis- 

 tinction in physiological character is one that is met with 

 throughout the Lepidoptera, and, of course, elsewhere in the 

 animal kingdom. Individuals belonging to the same family, 

 the same genus, the same species, even the offspring of the 

 same parents, are found separated into these two distinct 

 physiological classes. 



Regular response of one class. 



The first class — those that yield to temperature — seem 

 usually to respond to it with a regularity which is noteworthy, 

 in many instances all emerging to the very day. I give 

 examples, summer pupae of some common English species, 

 showing this.* (See Appendix, Table I.) 



Resistance of another class. 



As examples of the other class, that on which warmth is 

 expended in vain, we have such species as EucMo'e carclamines, 

 Araschnia levana (winter phase), Pieris brassicse (winter phase), 

 Selenia tetralunaria (winter phase), some experiments on most 

 of which are described later. 



I am not suggesting that the second class, those non-respon- 

 sive to temperature, are thus insensitive throughout their lives ; 

 the insensitiveness may be confined to certain metamorphic 

 stages, or even to certain periods comprised in those stages ; 

 when, for example, any of them shake off their long torpor 



* In my experience eggs of most Lepidoptera that are laid at one time 

 in summer hatch out nearly all together, in this respect differing greatly 

 from many of the wintered eggs, such as those of the genus Ennomos, 

 and of Liparis monacha, which usually spread their hatching over a very 

 long period with little regard to temperature. In this respect there is a 

 parallel between the egg and the pupa. 



