x PHYLUM ARTHROPODA 261 



smaller, simple eyes. The segments of the abdomen (seven 

 in number) are united together, being covered dorsally by a 

 continuous abdominal carapace. At the posterior end is 

 attached a very long, narrow, caudal spine (tels). The 

 anterior appendages resemble" those of the Scorpion. In 

 front of the mouth is a pair of short, three-jointed, chelate 

 appendages, the cheficerce. (1\ at the sides, of a labrum or 

 upper lip. Behind these follow a series of five pairs of legs, 

 the bases of all of which, with the exception of the last, are 

 covered with spines, and have the action of jaws, while their 

 extremities are for the most part chelate : between the sixth 

 pair of appendages is a pair of processes, the chilaria. The 

 first pair of appendages of the abdomen are flat plates, which 

 are united together in the middle line and together form the 

 broad operculum (operc), overlapping all the posterior appen- 

 dages ; on its posterior face are the two genital apertures. 

 The posterior appendages, of which there are five pairs, are 

 thin, flat plates to which the gills are attached ; each of them 

 is divided by sutures into a small inner ramus or endopodite, 

 and a larger external ramus or exopodite. 



In their mode of life the Arachnida present almost as great 

 a diversity as the Insecta. Some Acarida are parasites 

 throughout life. Most of the other groups of Arachnida 

 are predaceous preying for the most part on Insects or 

 other Arachnids. The primary function of the threads 

 formed from the secretion of the spinning organ is to 

 constitute the material for the manufacture of a cocoon for 

 enclosing the eggs, and in some Arachnids this is the 

 sole purpose to which they are devoted. In others there 

 is added a nest for the protection of the eggs and of the 

 parent itself; this in many cases becomes a permanent 

 lurking place which the Spider inhabits at all seasons, 

 and from which it darts out to capture its prey : in the 



