398 ox INSECT ANATOMY. 



understand why an insect hovering on the wing all day or darting 

 through the air like a dragon fly should not dry up altogether, 

 unless some provision existed for surrounding important organs with 

 fluid. That the common belief in the physiological inferiority and 

 anatomical imperfection of insect circulation is erroneous, further 

 appears from the consideration of other changes involved in the 

 *'fast life/' of our insect. And particularly from the oonversion of 

 the nutritious fluid into the remarkable series of products, secreted 

 by the glandular organs which receive their supplies from circulating 

 channels and lymphatic vessels. 



Silk, honey, wax, cochineal, cantharidine, formic, and other acids, 

 irritant fluids which excite disease in plants and animals, are all 

 suggestive of the subtle chemistry of insect secretion which thus 

 spreads good and evil upon the world around. The varieties of gland 

 and other peculiar arrangements of insect structure by which such 

 results are brought about, form therefore interesting points of 

 anatomical enquiry. 



There is yet another chapter of insect history, namely, parasitic 

 life,' which closely concerns us who sufl'er grievously from it, and 

 which is mainly elucidated by anatomical investigation. In all these 

 particulars the practical and scientific interests of mankind run 

 together, whether in finding remedies for the plagues which 

 ignorance of insect habits brings upon man, or in discovering the 

 causes of ravages which devastate his crops, or in improving the 

 management and increasing the productiveness of insects which 

 yield him valuable materials. In relation with these practical 

 issues stands the history of development and reproduction, which, so 

 far as anatomical investigation has been prosecuted in this direction, 

 reveals unsuspected facts, and leaves unexpected mysteries. The 

 altered conditions and habits of the insect and its changed functions 

 find equivalent expression in external •' ecdysis," and internal 

 "metamorphosis." But such revelations leave all unexplained 

 mysteries more mysterious than before — such for example as the 

 selection of place in which to deposit ova, immigration, and 

 social instincts generally. Nor is the study of insect sensation 



