414 AEACHNIDA 



jointed, the terminal joint being a sharp claw, near the end of which is the 

 opening of a poison gland. The mandibles are usually directed downwards 

 so that the spider must strike when its prey is beneath it. The second 

 pair of appendages are the pedipalps or palpi, which are leg-like in form 

 and composed of six segments; the large and flattened basal segments 

 of these are called the maxillae or endites and extend forwards, forming 

 the principal jaws of the animals, being used to chew or squeeze the 

 food. 



In the male the end of the pedipalp is enlarged and bears the 



more or less complicated palpal organ by which sperm is conveyed to 



the female in the act of pairing (Fig. 653, C). The four pairs of long 



walking legs are seven- jointed. The tarsus or terminal joint of each leg 



bears a pair of claws, the inner edge of each of which is toothed ; in many 



spiders a third smaller claw is also present and in others a thick brush of 



hairs. Between the maxillae is a plate called the labium or lip, and 



between the base of the legs is the sternum. The abdomen bears at 



its hinder end, just in front of the anus, usually 3 pairs of spinnerets, 



which are modified legs (Fig. 655). At the end of each spinneret are 



minute tubes which are the ends of the ducts of the silk glands; the 



fluid silk coming out of these tubes unites to form a single strand, and 



hardens on exposure to the air. In a few families a plate called the 



cribellum lies in front of the spinnerets from which spinning tubes also 



project; such spiders have a row or comb of stiff hairs on each of the 



hind legs called the calamistrum (Fig. 655) by means of which a band of 



silk may be spun. All the spinning tubes do not exude the same kind 



of silk, but a variety of kinds is produced which are used for various 



purposes, as for making the different parts of the web, nests, cocoons, etc. 



Spiders are not well provided with special sense organs. The long 



legs and the hairs usually covering the body are tactile organs, and in 



most spiders eight simple eyes are present on the front portion of the 



cephalothorax usually in two rows, enabling the spider to see a short 



distance (Fig. 653, B). 



The respiratory organs of spiders consist of two pairs of lungs in 

 the Tetrapneumones, which are situated in the forward part of the abdo- 

 men and open to the outside by slit-like spiracles on the ventral surface; 

 in the Dipneumones one pair of lungs is present and a pair of tracheae, 

 the latter opening in most cases through a single spiracle in front of 

 the spinnerets. Each of the lung spiracles is covered with an integu- 



Emerton, 1902. "Families and Genera of the Araneida," by Nathan Banks, Am. Nat, 

 Vol. 34, p. 293, 1905. "Fauna of New England. A List of the Araneida," by Eliza- 

 beth B. Bryant, Bost. Soc. Nat. Hist., Occ. Papers, No. 7, 1908. "Catalogue of Neartic 

 Spiders," by N. Banks, Bull. No. 22, U. S. Nat. Mus., 1910. "The Spider Book," by 

 J. H. Comstock, 1912. 



