'216 ORDER PULMONARIA. SPIDERS, ETC. 



we never find more than two or four. Some of these animals, 

 known under the name of False- Scorpions, very much resemble 

 Spiders, and are remarkable for the length of their limbs ; others 

 have the mouth formed for sucking, and constitute the family of 

 AcaridcB, or Mites. 



ORDER I. PULMONARIA. 



752. By the characters just now stated, this order may be 

 divided into two sections ; the ARANEIDA, or Spiders, having 

 small foot-like palpi, not terminating in pincers ; and the 

 PEDIPALPI, or Scorpions and their allies, having very large palpi, 

 which terminate in pincers or large hooks. 



753. Section I. ARANEIDA. The Arachnida of this group 

 all agree, more or less closely, with the common Spider, in their 

 form and structure. Their cephalothorax appears as if composed 

 of but a single segment, and is covered with a sort of horny 

 buckler, usually of oval form ; the abdomen is appended to it by 

 a very short footstalk, and usually consists of a soft and tumid 

 mass. The eyes are nearly always eight in number ; although 

 there are sometimes but six. The mandibles terminate in a very 

 sharp moveable hook, which is pierced near its extremity by a 

 small aperture, serving as a passage for the poison secreted by a 

 gland lodged in the preceding joint. The legs are inserted 

 almost in a circular manner around the cephalothorax (Fig. 439) ; 

 they are all of nearly the same form ; and each of them is com- 

 posed of seven joints, the last being armed with two hooks, 

 which are commonly toothed like a comb. The pulmonary sacs 

 in this order are only two in number, or may even be reduced to 

 a single one ; they are placed near the base of the abdomen, and 

 their position is indicated externally by a brownish or whitish 

 spot. All the members of this section are provided with spin- 

 nerets ; but it is only in a comparatively small number, that we 

 find the power of constructing silken webs of any great extent. 

 The ARANEIDA are divided by M. Walcknaer, who has made 

 this group his especial study, into families, according to the 



