﻿348 j. DEWITZ — THE BEARING OF PHYSIOLOGY 



consequence of the action of these temperatures upon the organism, there are 

 changes which demonstrate themselves in the coloration of the blood and which 

 begin even at such low temperatures as 40°-41° C. with an exposure of 15 

 minutes. If the exposure at this temperature be prolonged to 40 minutes the 

 insect larvae can still completely recover, but their ultimate survival becomes 

 uncertain. There is no need here to pursue the application of these experiments 

 to natural conditions, for such temperatures as we have utilised in the foregoing 

 investigations occur everywhere in summer in the open. Their influence lies at 

 the root of manifold changes depending upon local conditions." 



I may be allowed to adduce an example in illustration of the effect of heat 

 upon insects. A large number of larvae of the blow-fly, Calliphora vomitoria, 

 which were ready for pupation, were kept for 70 minutes in a heat of 40-41° C. 

 under appropriate conditions of humidity. Of the 196 larvae which survived 

 that treatment only 53 became normal pupae, and of the latter 41 became 

 flies. Under the influence of heat changes take place in the blood and these 

 changes affect the tyrosinase contained therein, an oxydase which plays an 

 important part in the pigmentation and metamorphosis of insects, as I have 

 endeavoured to demonstrate in various publications bearing on that subject. 

 These are enumerated in the bibliography under No. 10. 



The cold of winter, on the other hand, when within normal limits, does not 

 injuriously affect insects ; in fact it rather promotes their future well-being. 

 Only when cold occurs suddenly after mild temperatures or out of season does it 

 become fatal to insects. On certain species however cold has a peculiar effect 

 which is equally observable in normal winter time as in the colder regions of 

 high mountains or in the Arctic regions. Such insects, and the females in 

 particular, become wingless. This apterism is specially noticeable with 

 Lepidoptera and Diptera of Alpine and of polar regions. The wingless state 

 of the female of our winter-moth {Chcimatobia brumata) is well known, and the 

 knowledge of this fact has given rise to the use of the glutinous belt which 

 is fastened round fruit trees in order to prevent the wingless females from 

 climbing up the trunks. 



Insects may also be made wingless by artificially refrigerating their pupae and 

 nymphae, a fact already recognised by several experimenters who have tried 

 to produce colour changes in butterflies by means of high or low temperatures. 

 Occasionally also bee-keepers have observed that after an abnormally severe 

 winter the bees were wingless. I have occupied myself particularly with these 

 phenomena and have come to the conclusion that wingless insects result only when 

 cold is applied to pupae and nymphae. Cooling or heating of larvae yielded 

 insects with normal Avings. According to my interpretation of these observations 

 the abnormal temperature would injuriously affect the oxydase (tyrosinase) which 

 is found evenly distributed throughout the whole organisation of the larva but 

 is concentrated in the wings of the pupa. If we take, for instance, a pupariuni 

 of Calliphora vomitoria in which the still white pupa is enclosed and place it in 

 alcohol, ether or chloroform, we obtain a white pupa with brown wings. Such 

 however does not occur with previously boiled pupae, the enzyme therein having 

 been destroyed by the high temperature. 



