XII] 



SPIDER 



263 



The silk is secreted by a large number of glands which have 

 their exit at the above-mentioned pores. Of these in E. diademata 

 there are five different sorts and each secretes a special kind of 

 thread ; for the various lines in a Spider's web differ considerably 

 one from another, in accordance with the use they are put to. 

 The circular lines are sticky and help to catch insects for the 

 Spider's food, the radial lines are stout and form a framework for 



3 4 



Fio. 116. 



FIG. 117. 



Fm. 116. Horizontal section through the abdomen of a Spider, Argyroneta. 



After MacLeod. Magnified. 



1. Opening to exterior, tracheal stigma. 2. Terminal tracheae. 



3. Lateral tracheae. 4. Lung-books. 



FIG. 117. Longitudinal section through the lung-book of a Spider. Magnified. 



From MacLeod. 

 1. Opening to the exterior or stigma. 2. 



leaves. 3. Space in which the air circulates. 



the blood circulates. 



Free edge of the pulmonary 

 4. Space in which 



the support of circular lines ; the threads with which the Spider 

 binds up its captured prey differ from these, and there is still 

 another kind of thread with which it constructs its cocoons, and 

 each kind of line is supplied from different sets of glands. 



The dissection of a Spider requires much care, since the organs 

 almost fill the body and are completely embedded in the large 



