4IO ZOOLOGY 



are four conical two -jointed spinnerets, whose apices meet 

 together when at rest ; if these be separated, two smaller 

 single-jointed spinnerets are disclosed. Each of these projec- 

 tions is very mobile, and they can be separated and approximated 

 with ease. They are perforated at their apices by a number 

 of minute pores, amounting to about 600 in all, through which 

 the " silk " leaves the body. This silk is secreted by an enor- 

 mous number of glands which lie in the abdomen ; these in the 

 species in question are of five distinct kinds. Each kind of 

 gland has not only a definite relation to the spinnerets, some 

 supplying two pairs and others only one, but the threads 

 secreted from the various kinds of glands differ in quality, and 

 are used for different purposes. Thus the lines in the con- 

 centric threads of the well-known wheel-like webs differ from 

 the radial lines in being sticky, and so serving to hold the 

 captured flies, etc., and these again differ from the threads 

 which form the cocoon, or from those used to bind up captured 

 prey ; and each of these various kinds of thread is the product 

 of one definite set of glands. 



Between and a little behind the posterior spinnerets the 

 anus is situated. 



In Efeira the two stigmata leading to the pulmonary sacs 

 are on a level with the genital orifice. The cavities of the two 

 pulmonary chambers are in communication with one another 

 across the median line. Each cavity is to a great extent 

 occluded by a number (about sixty) of horizontally placed 

 lamellae, which are attached as a rule to the wall of their 

 sac by their anterior and lateral edges, but present a free 

 edge posteriorly. These lamellae have very thin chitinous 

 walls, which are prevented from collapsing by the presence of 

 a number of little cellular pillars. Between the dorsal and 

 ventral wall of each lamella the blood circulates, whilst the 

 air passes in the slit -like spaces between the neighbouring 

 lamellae. 



In addition to the pulmonary sacs, Epeira also has a 

 tracheal system. A single stigma opens just in front of the 

 anterior spinnerets, and leads into a median sac ; from this 

 four tracheae emerge. These are chiefly distributed to those 

 organs which lie behind the pulmonary sacs. In other species. 



