452 



ARTUKOPODA. 



organs and with the basal maxillary process to comminute the 

 food. In the male the pedipalpi have the terminal joint swollen 

 to a pear-shaped structure (fig. 469) by which the sexes are easily 



FIG. 468. FIG. 469 FIG. 470. 



FIG. 468. Latrodectes macfmis,* poison spider. (After Marx.) 

 FIG. 469.- Pedipalp of Pardosa uncnta. (After Emerton.) 



FIG. 470. Spinnerets of Epeira diadema. (After War burton.) 1, 2, 3, first, second, 

 and third spinnerets; /, threads. 



distinguished. This is used to convey the spermatozoa to the 

 female, a rather dangerous process, as the male is apt to be killed 

 by the much stronger mate. 



At the hinder end of the abdomen, just in front of the anus, 

 are the spinnerets, which are reduced appendages, as is shown by 

 their paired arrangement and their jointing (fig. 470), as well as 

 by development. They are truncate and have at the tip a ' spin- 

 ning field' from which numerous minute, two-jointed spinning 

 tubes, resembling hairs, arise, each of which is the end of a duct 

 of a silk gland. Different kinds of glands, producing silk for differ- 

 ent purposes, occur. The number of spinnerets varies between two 

 and three pairs, and in front of these may be an unpaired spinning 

 region, the cribrellum, so that hundreds or even thousands (Epei- 

 ridae) of glands may be present. 



The secretion of the glands hardens in contact with the air, and the 

 single threads are united by the combs of the hinder feet, into a larger cord 

 which can be regulated in size according to the number of glands which 

 are active. Yet the largest cord is finer than the finest silkworm silk, 

 hence it is often used for the cross-hairs of telescopes. The spider silk has 

 many uses; it is used to line the nests, to form cocoons for the eggs, as a 

 means of descent from high places, and to form the well-known webs. 



The nervous system consists of a brain and a circumoesophageal ring, 

 and, in the Mygalidae, a single abdominal ganglion. The arrangement of 

 the six or eight ocelli and the relative lengths of the legs are matters of 

 systematic importance. Two pairs of respiratory organs occur. In the 

 Tetrapneumones there are two pair of lungs, but in the Dipneumones the 



