448 THE NATURAL HISTORY 



constituted, is founded on other characters in addition 

 to these, for example, in true insects the head, thorax 

 and abdomen are distinct, the number of legs is never 

 more than six, the eyes are compound, and the res- 

 piratory apparatus consists of tracheae and spiracles, or 

 breathing pores. These conditions are so far modified 

 in the few remaining subjects which will occupy our 

 attention, that the establishment of other classes for 

 the reception of the latter has been found necessary, 

 and the first to come under our notice is that which is 

 made up of Spiders, Scorpions and Mites.* 



In true Spiders the antennae, which, as we have 

 seen, play such an important part in the economy of 

 insects, are altogether absent, the body is divided into 

 two segments only, the cephalo-thorax consisting of 

 the head and trunk together, undistinguishable from 

 each other and the abdomen, which is destitute of 

 insections. They possess eight legs, two, six or eight 

 simple eyes, and they breathe by means of pulmonary 

 sacs and stigmata. Although it is well known that 

 spiders prey on various insects, either by actively 

 hunting them down, or by entrapping them in nets 

 which they ingeniously hang up for the purpose, much 

 difference of opinion exists among those who have 

 investigated their structure and closely studied their 

 habits, as to the anatomical details, uses and mode of 

 action of the several organs with which they are fur- 

 nished. Some doubt that spiders are venomous, and 

 others believe that each of the fine threads, of which 

 their webs are composed, is a single homogeneous line, 

 but the preponderance of authority is in favour of the 

 theory that spiders are really capable of injecting a 

 poisonous fluid into the wounds they make, and that 

 their threads are very complex indeed. Their offensive 

 weapons, representing mandibles, are two-jointed or- 

 gans situated above the mouth and technically called 



* Class ARACHNIDA. From the Greek, arachne, a spider, 



