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ANIMALS 



communicate with the second smaller portion of the stomach 

 by means of short ducts. Digestion proper takes place in this 

 portion of the digestive tract. A narrow intestine of simple 

 structure leads to the vent at the posterior end of the abdomen. 

 459. The function of salivary glands is primarily to 

 moisten the food preparatory to swallowing. Consequently 

 they are only necessary in terrestrial animals. The so-called 

 salivary glands of nereis owe their name to their position and 



Fig. 1 10. — Digestion and circulatory systems of the crayfish. Upper figure: 

 a, Mouth; ,b oesophagus; c, cardiac portion of stomach; d-e, pyloric portion of 

 stomach; e, opening of digestive gland; /, intestine; g, vent; //, digestive gland 

 ("liver"); i, heart; j, gonad; k, brain; /, /, ventral nerve cord. Lower figure: 

 a, Heart; b, dorsal abdominal artery; c, sternal artery which branches into the 

 ventral abdominal and the ventral thoracic arteries; d, ophthalmic artery; 

 e, antennary artery; /, hepatic artery; g, blood sinuses; h, afferent branchial 

 vessels; i, efferent branchial vessels. 



must not be supposed to be in any sense true salivary glands. 

 No such glands occur in the crayfish, but in the terrestrial 

 Arthropods, the Insects, they are generally found. The mouth 

 parts in Insects consist of three pairs of appendages. There 

 is an oesophagus, into which the salivary glands open. Some- 

 times the oesophagus is enlarged to form a crop. Sometimes 

 there is also a gastric mill analogous to that of the crayfish. 

 Then follows the true stomach which has numerous small 



