42 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to that of the surrounding air, the observations covering a large range of 

 temperatures. He prefixes to his paper a very elaborate historical survey, 

 showing how very varied are the results arrived at by different investi- 

 gators on the subject, and concludes that these discrepancies are due ou 

 the one hand to variation in the insects themselves, dependent on locality, 

 food, age, sex, &c, and on the other to the nature of the apparatus em- 

 ployed. His own apparatus is based on the principle of thermo- 

 electricity, changes of temperature being measured by variations of 

 electrical current as indicated by a sensitive galvanometer. The insect 

 is connected with the instrument by means of a fine thermo-electrical 

 needle sunk in its body. The insects employed were taken in Bulgaria, 

 and the experiments were based upon the natural variations in tempera- 

 ture to which insects living in the spscial locality are subjected. 



The experiments show that resting insects have the same temperature 

 as their surroundings, and can tolerate a very wide range of variation 

 without injury. Moving insects have a temperature higher than that of 

 the surrounding atmosphere. If the temperature of the medium is con- 

 tinuously raised, the insects display active movements as their body- 

 temperature rises to 39°, and die when it reaches 46°-47°. When the 

 temperature of the air is gradually lowered, the body-temperature sinks 

 continuously, sometimes to about — 15° (the normal freezing point of the 

 coelomic fluid or " critical point "), then rises suddenly, usually to about 

 — 1*5°. If the lowering of temperature be still continued, the body- 

 temperature then again sinks slowly. If the cooling be continued until 

 the body-temperature sinks for a second time to that at which the sudden 

 rise previously took place (that is to the " critical point "), then death 

 ensues. The temperature of the " critical point " is not constant, even 

 for the same species, but varies with various conditions. Thus it is 

 lowered in fasting insects, and in insects which have been repeatedly ex- 

 posed to low temperatures (cf. the natural conditions to which insects are 

 exposed in winter). The general phenomena exhibited by insects ex- 

 posed to low temperatures are all explicable on the same principles as 

 the phenomena displayed by water in capillary tubes, or by citric acid in 

 porous vessels, when exposed to similar temperatures. Further, in 

 general the relation of insects to low temperatures is such as it might be 

 expected the process of natural selection would produce in organisms 

 which are unable, like birds, to escape cold by their own activity, and are 

 unprovided with any external means of defence like the hairy coat of 

 mammals. The adaptation in general is such that the insects are able to 

 adjust their own temperature to that of the surrounding medium, and 

 to maintain life under most natural variations of temperature. 



Larva of Microdon mutabilis.* — E. Hecht has studied this inter- 

 esting form (one of the Syrphidge) which frequents the nests of ants. 

 The adult is not peculiar, but the larva is remarkably like a little slug. 

 Indeed, it has been referred to Purmula and to Scufelligeral Hecht 

 shows that the convergence, if it deserves the name, is wholly super- 

 ficial. He describes the complicated elaboration of the chitinous cuticle. 

 He also notes that in this form at least the muscle-fibres do not enter 

 into relation with the epidermic cells, but are in intimate continuity with 

 the cuticle. 



* Arch. Zool. Expe'r., vii. (1899) pp. 3G3-S2 (1 pi.). 



