48 



PHYSIOLOGY OF THE INVERTEBRATA. 



labiuii. Malpighian tubales are also sometimes present. 

 The alimentary canal terminates in an anus which is either 

 situated at the posterior end of the body or near the middle 

 ol the abdomen. 



Fig. 9. — Altmkntary Canal of Macrobiotus. 



a — mouth or oral cavity. /' = salivary duct. c = salivary gland. 

 h — oesophagus. d = pharynx. e = alimentary tract or intestine. 

 / — anus, g = microscopical structure of salivary gland. 



(17) The Araneina are Arachnida with sub-chelate 

 cheliceras, and possess a poison gland which opens in the 

 terminal joint. They have from four to six spinning glands 

 situated at the posterior end of the abdomen. 



" The spiders are remarkable for the minuteness of the 

 pharynx and oesophageal canal. Savigny believed that in 



