314 THE entomologist's record. 



produced under the one condition as under tlie other, althougli in an 

 opposite direction. 



So far then we see that a change made in the environment of the 

 pupa must necessarily produce some effect on develojiment. If the 

 change he suftieiently extreme, then the effect is death ; anything short 

 of such an extreme will produce an effect proportioned to its magnitude. 

 If a pupa be thoroughly acclimatised to a given range of temperature, 

 then excessive heat or cold must be injurious. The variability of our 

 climate renders it certain that few species are perfectl}'' acclimatised, and 

 that, therefore, a moderate range of temperature has but little actual 

 effect on them, something considerably beyond the ordinary mean 

 range being necessary for this j^urjiose. 



It has been suggested to me with regard to acclimatisation that it 

 must be borne in mind that some species do l)etter in cold, others in 

 hot, some in wet, others in dry seasons. Whether this be due to the- 

 fact that some of our insects have spread to us from more northern, 

 others from more southern latitudes, or to other causes, it renders it 

 probable that the same amount of heat may act prcjudicialh' on one- 

 insect and advantageously on another. In the latter case increased, 

 heat ma}'' be expected to produce effects due to an increase of vitalit}', 

 whilst in the former cold Avill produce the same result. A great 

 excess of either would, of course, be injurious to any species. To an 

 insect that exists here say in a mean temperatin-e of 54° but prefers 

 60°, any decrease of temperature will be injurious, but increased 

 temperature will not effect it iirejudiciall}' until it exceeds 60°, probal:)ly 

 not until it exceeds 66°. 



It has also been suggested that an insect may have been trained by 

 " natural selection " to assume a particular form at 50'^, another at 60^^ 

 another at 70" and so on, and that this may be an element in the 

 production of dimorphic or trimorphic seasonal forms. • 



Are not the results foreshadowed in the above considerations found 

 in Mr. Merrilield's specimens ? Do not a large percentage of his sjieei- 

 mens exactly fulfil these conditions"? The colour, the scaling, the 

 wing membrane in almost all those that are subjected to extremes in 

 either direction of heat or cold have suffered ; sometimes all three 

 characters are markedlj'- abnormal in the same specimen. 



Now with regard to the direction in which the colour of the imago 

 will vary according as the pupa is subjected to heat or cold. In the 

 Introduction to Brit. Nocino' and their Vars., vol. II., pp i-xxiv., I haAO 

 detailed a large numljcr of facts and experiments with regard to insect 

 colours and have made suggestions as to their serpience and relation- 

 ships. Tlie colours of insects are, I take it, largely dependent on three 

 things : — (1). The pigment in the scales themselves. (2). The shape,. 

 &c. of the scales (giving rise to the non-pigmentary colours). (3). The 

 colour of the wing membrane. The relationship of all these must 

 be considered if we are to get any true idea of the changes which the 

 colours of insects undergo when exposed to abnormal temperatures, and 

 there can be no doubt that all three are affected b}' Mr. Merrifield's 

 treatment. 



It follows, from the physiological details enumerated above, that the 

 colour may be affected in any of these directions. (I). The pigment 

 may fail in whole or in part. In this case the ground colour of the base- 

 ment membrane of the scale itself maj' replace the ordinary colour ; 



