ARANEIDA. 



815 



(Fig. 535, Or) ; from this silk also issues and its presence is always 



correlated with that of the calamistrurn on the last pair of legs. 



Some spiders have the power of making sounds and these are 



produced by certain comb-like structures being drawn over 



Fia. 536. The Garden Spider. Araneus (Epeirn) di'idematus, sitting in the centre of its 



web (after Blanchard). 



others of a file-like nature. These stridulating organs are 

 situated either between the cephalothorax and abdomen or 

 between the chelicerae and the pedipalps or between the pedipalps 

 and the anterior legs, all parts of which are movable upon one 

 another. 



Spiders take only liquid food and the mouth is minute and very 

 difficult to find, being concealed by an under-lip or labium. It 

 opens into a fine oesophagus which runs dorsalwards and dilates in- 

 to a large sucking-stomach (Fig. 537, 2). The whole of these struc- 

 tures are lined by chitin and are stomodaeal. From the walls of 

 the stomach stout muscles run to the tergum of the cephalothorax 

 and to the endosternite, a plate-like endoskeleton which under- 

 lies the stomach. When these muscles contract the lumen of 

 the stomach is enlarged and fluid is sucked into it. The stomach 



