ORDER PUIMONARIA. SPIDERS, ETC. 



ORDER I. PULMONARIA. 



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

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

 small simple palpi, not terminating in pincers ; and the PEDI- 

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

 which terminate in pincers or large hooks. 



824. 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. 546) ; they 

 are all of nearly the same form ; and each of them is composed 

 of seven joints, the last being armed with two hooks, which are 

 commonly toothed like a comb. The pulmonary sacs in this 

 order are usually 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 small number that we find the power 

 of constructing silken webs of any great extent. The ARANEIDA 

 are divided by M. Walckenaer into families, according to the 

 arrangement of the mandibles and eyes, which corresponds very 

 remarkably with their respective modes of life.* These families, 

 and their principal subdivisions, are as follows : 



* For this reason, the classification and nomenclature of Walckenaer, 

 although now somewhat antiquated, are retained here. 



