150 



A COURSE ON ZOOLOGY. 



poisonous liquid secreted by a gland situated at the base 

 of the organ. A pair of jaw-feet with six joints com- 

 pletes the buccal apparatus. 



The digestive apparatus consists of a narrow, cylin- 

 drical oesophagus, opening into a large pocket, which 

 empties into a second stomach 

 that is followed by the intestine. 



Respiration is effected by means 

 of tracheae, some of which are so 

 enlarged as to form a kind of 

 lungs, and hence the respiration 

 of spiders is sometimes called 

 pneumotrachean, to distinguish 

 them from other arachnida whose 

 respiration is purely trachean, 

 like that of insects. 



The circulation, as in insects, is 

 accomplished by means of a dorsal 

 vessel that supplies the arteries, 

 the venous blood circulating in 

 interorganic lacuna}. 



The nervous system of the 

 arachnida consists of two gan- 

 glionic masses, a cephalic ganglion, 

 situated above the oesophagus, and 

 a thoracic ganglion, placed below 

 it. The latter represents the 



thoracic and abdominal ganglia joined in one, and sends 

 nerves to the legs and to the abdomen. This coalescence 

 of ganglia occurs in some crustaceans and also in some 

 insects ; it is not characteristic of spiders. 



Spiders reproduce their species by means of eggs, from 

 which the young creatures are hatched directly without 



DIGESTIVE APPARATUS OF 

 SPIDER. ce, oesophagus ; a, 

 stomach ; b, ramifications 

 of the stomach ; d, intes- 

 tines ; e, glandular tubes ; 

 /, rectum ; c, urinary ca- 

 nals. 



