ARTHROPODS. CLASS ARACHN1DA 145 



larger species, which measure five or six inches in length, 

 may produce certain disorders chiefly affecting the circula- 

 tion. In this country there are upward of thirty species, 

 most of which are comparatively small. 



136. The harvestmen. The harvestmen or daddy-long- 

 legs are small-bodied, long-legged creatures which resemble 

 in general appearance several of the spiders. They differ 

 from them, however, in the possession of claws correspond- 

 ing to the smaller ones of the scorpion, and in their method 

 of respiration, which is similar to that of insects. During 

 the day they conceal themselves in dark crevices or stride 

 slowly about in shaded places ; but at night they emerge 

 into more open districts and capture small insects, from 

 which they suck the juices. 



137. The spiders. The spiders are world-wide in their 

 distribution, and are a highly interesting group, owing 

 chiefly to their peculiar habits. Examining any of our 

 familiar species, it will be seen that the united head and 

 thorax are separated by a narrow stalk from the usually 

 distended abdomen. To the under side of the former are 

 attached four pairs of long legs, a pair of feelers, and the 

 powerful jaws supplied with poison-sacs, while eight shin- 

 ing eyes are borne on the top of the head. On the abdo- 

 men, behind the last pair of legs, are small openings into 

 the lung cavities which contain a number of vascular, leaf- 

 like projections known as lung-books. In some species 

 a well-marked system of tracheae are also present. At the 

 hinder end of the body are four or six little projections, 

 the spinnerets, each of which is perforated with many 

 holes. Through these the secretion from the glands be- 

 neath is squeezed out in the form of excessively delicate 

 threads, often several hundred in number, which harden on 

 exposure to the air. According to the use for which these 

 are intended, they may remain a tangled mass or become 

 united into one firm thread ; and according to the habits 

 of the animal, they may be used for enclosing their eggs, 



