424 THE CANADIAN NATURALIST. [Dec. 



duced by-these spiracle appendages, during the rapid ingress and 

 egress of the air ; an effect similar to that which is produced by 

 the sweeping of the air over the strings of an eolian harp. 

 The most important vital purpose, however, is doubtless 

 that to which I have already alluded — the protection afforded to 

 the air vessels within. There is also another important end 

 which they may serve, and one which, 1 think, has not been 

 observed by any writer on the subject. It is this : the modifica- 

 tion of the temperature of the air, as it enters the trachea, and 

 the preservation of that within the body, at the normal standard 

 of heat, usually existing in the different members of this class. 

 For this purpose these fringes and plates and membranous folds, 

 would be admirably adapted, and would act in precisely the same 

 way as the metallic framework of a respirator does when 

 worn by consumptive persons. A question might here naturally 

 arise, as to the production and maintenance of animal heat in the 

 insect economy. But the full discussion of this subject would 

 demand more time than we have at disposal. Many interesting 

 observations have been made, which show that the temperature of 

 different insects varies greatly, especially those living in societies 

 (as the hive bee) whose normal standard of heat is very much 

 higher than that of other classes. There has been a prevailing 

 notion that the temperature of insects is altogether regulated by 

 that of the external atmosphere in which they live, but this opinion 

 is, I think, at variance with the common principles of animal 

 physiology; and it is, moreover, contradicted by a variety of 

 experiments, bearing on this questien. There can be little doubt, 

 I think, that the standard of heat, in different species of insects, is 

 regulated very much by the degree of muscular activity mani- 

 fested by them ; for this would involve a more rapid and vigorous 

 respiration, and a greater consequent evolution of heat. Without 

 pursuing this question farther, however, I would remark finally 

 respecting the spiracles of insects, that however beautiful and 

 elaborate they may be in their structure, and however perfectly 

 adapted to the habits and peculiarities of the creatures possessing 

 them, they are but the portals to an inner sanctuary of wonders, 

 unspeakably transcending all human contrivances in execution, 

 and surpassing human thought, even in conception. The fact 

 that insects breathe, and that their respiration is carried on by 

 means of an elaborate system of air tubes, which ramify extensive- 

 ly through the interior of their body, has long been known, and 



