BIOLOGY. 273 



he made a modification necessary for his experiments. One of 

 the bulbs presents a deep interior cavity, so that the volume of 

 air contained, in the concentric zone is equal to that of the volume 

 of air in the other bulb. The contracted orifice is closed by a 

 cork furnished with a tube, through which air enters and escapes 

 freely. The insect to be experimented on is introduced into this 

 cavity with the precautions necessary to avoid falsification of the 

 result. M. Giraud has also employed thermo-electric needles 

 formed of iron and copper, or, still better, of iron and platinum, 

 such as already, in the hands of M. Becquerel, have done good 

 service in the study of animal heat. Lastly, M. Giraud has used 

 the theromo-electric piles of bismuth and antimony. 



Some of M. Girauci's conclusions are as follows: Adult insects, 

 even when sleeping or very weak, never present a diminution of 

 the temperature of the surface of their body below the surround- 

 ing temperature. The larvae and pupae of insects, with an im- 

 perfect metamorphosis, behave, in this respect, like the adults. 

 Like them, they always present an elevation of temperature above 

 that of the surrounding air, or at least a temperature equal to 

 that of the latter. This is not always the case in insects with a 

 complete metamorphosis. The author has frequently ascertained, 

 in caterpillars with smooth bodies, that the surface descends be- 

 low the temperature of the surrounding air, which shows that the 

 evolution of heat by the respiratory combustion may be insuffi- 

 cient to compensate for the loss due to superficial evaporation or 

 cutaneous transpiration. The same fact occurs in chrysalids. 

 The cocoon with which the pupae of a great number of Lepidop- 

 tera and Hyrnenoptera envelop themselves serves to prevent a too 

 rapid desiccation of the animal, which would superinduce a fatal 

 superficial refrigeration. In fact, pupre present a distinct eleva- 

 tion of temperature at the moment when they are taken out of the 

 cocoon; then, in the air, they lose their weight by evaporation, 

 and the surface of their body often descends below the tempera- 

 ture of the surrounding air. In winter naked torpid caterpillars 

 and pupae return to the surrounding temperature, or to a very 

 slight excess above it. The superficial refrigerations due to 

 evaporation are not produced when the temperature very nearly 

 approaches 32 F., a result perfectly conformable with the re- 

 sults of physical researches. 



Sex exerts a marked influence on the evolution of superficial 

 heat in certain groups of insects. Thais in the Bombycidse the 

 males are warmer than the females. Something of the same kind 

 seems to occur among the Phryganidae and Pieridce. But we 

 must be careful in generalizing these results. In caterpillars the 

 heat is not localized in a few segments, but belongs to all, which 

 agrees well with the analogous dissemination of the nervous 

 centres. This is by no means the case in insects with powerful 

 aerial locomotion. The variation of temperature shown by them 

 between the thorax and the abdomen may become very consider- 

 able. In the humble-bees, and especially in the Sphingidce, whose 

 flight is so powerful, the excess of the thoracic over the abdominal 

 temperature amounts commonly to from 7 to 11 F., or even 



