ON INSECT ANATOMY. 397 



yariety of life-habit but also in speciality of organs, and even in 

 special perfection of individual tissues. For instance, the muscular 

 energy transcends anything known of other animals. Attached to 

 the strong dermo-skeleton, it enables the insect to resist crushing 

 ■weights or to lift and drag them, to burrow into wood, to crush 

 stone and even metal, with contractile force that would not be 

 credited but for repeated trustworthy observation. Strength is not 

 however its only property, for rapidity of contraction is such that 

 the flight of a dragon fly or even a common house fly cannot be 

 equalled by bird or beast. And the compound effect of strength 

 and rapidity of action is manifested in leaping powers which no 

 other animal exhibits. Anatomy shews, in fact, that insect muscle 

 is the most perfect of known muscle tissues. But, further, this 

 expenditure of muscular power implies correlative power of 

 nutrition and excretion. Anatomy shews that the peculiar 

 respiratory system of the insect converts the whole creature into a 

 lung, and at the same time into a drainage apparatus, the excreta 

 being gaseous. With respect to nutrition, the replacement of used 

 up force argues the necessity of rapid assimilation for the ordinary 

 expenditure rather than of stored up material, but the fatty tissues 

 of the insect are very remarkable as a store of oxidisable fuel in 

 concentrated bulk. The possible capacity of nutrition is, however 

 shewn during the periods preparatory to metamorphic changes, 

 when the amount of food taken, and increase of vveight, are 

 unparalleled in the history of any other creature. In the active 

 phases of insect life, circulation is also more complete and special 

 than is commonly supposed; not only do all cavities and 

 interstitial spaces between the organs serve as blood channels, but 

 the nerve trunks and ganglia are enclosed in sheaths which I 

 consider equivalent to blood vessels or lymphatics, through whose 

 walls interchange of fluids takes place, besides which, many of the 

 finely ramifying trachese are apparently enclosed in canals filled 

 with the circulating fluid. Considering, indeed, the penetration of 

 every tissue of the body by terminal membranous tracheae and the 

 rapidity of aeration and gaseous exchange, it seems difficult to 



