36 CHAPTERS ON THE NATURAL HISTORY 



to other classes of the animal kingdom and their mutual rela- 

 tions, no subject is more interesting than is that of parasitism. 

 It occurs in almost all the orders, but in very different degrees. 

 Whole groups are naturally epizoic, others entozoic, while a few 

 (such as fleas and bed-bugs) can scarcely be arranged in either of 

 these divisions, inasmuch as, although in one sense epizoic, it ap- 

 pears probable that they may occasionally be able to go through 

 the whole of their life cycle without contact with the animals to 

 which they otherwise appear especially attached." This is a very 

 large and far-reaching subject, really a special department of en- 

 tomology, and one, in some of its aspects, of great economic im- 

 portance, and purely scientific in others. 



Not a few insects are endowed with luminous powers, such as 

 the fire-flies, cucullos, and some of the larval forms. The study 

 of this extraordinary property is likewise deserving of the closest 

 attention of the student. A variety of insects puncture all the 

 various parts of trees and plants, giving rise to peculiar growths 

 known as galls; but why these growths take place there has as 

 yet been no satisfactory explanation. 



The anatomy, classification, and geographical distribution of 

 the insects found even within the boundaries of this country are, 

 each and all, altogether too extensive subjects to be touched 

 upon in a brief popular chapter about them, so the remainder of 

 my space 1 will devote to short accounts of some special forms. 

 Spiders and their allies, for example, constitute a very large 

 group of insects; indeed, naturalists have created an entire sub- 

 class to contain them. They are designated as the Amelia iria, 

 and, as thus assembled, not only all the hosts of spiders in The 

 world are included in it, but also their near kin, the scorpions, 

 mites, daddy-long-legs, and the like. Much is already known 

 about them; about their habits and geographical distribution; 

 about their physiology and structure, and a great deal else. 

 Scientists have written many treatises about them, and a great 

 many have been beautifully drawn, colored, and given to the 

 world on handsome plates. Yet, notwithstanding all this, it may 

 be said that we have barely gained an insight of what we really 

 ought to know about them and, in the ages to come, no doubt 

 will. An entire history of this great sub-class of insects would 

 make a large library of itself, and men have lived who have de- 

 voted their whole lives to the study of only certain families of 

 spiders. Many years ago, the writer had a good friend who was 



