148 



Comparative Animal Physiology 



ous diverticula, the functions of which vary greatly. They may simply increase 

 surface for intracellular digestion, as in most clams, brachiopods, and starfish. 

 In arachnids and many snails they function in both intracellular and extra- 



Hepafopancreas Ventrccle of heart 



Stomach 



Esophagus 



Salivary glonds 



Mid-gut 



Hind-gut 



Posterior intestine 



Posterior 



odduclor 



Fig. 29. Diagrammatic representation of digestive tract in various animals: A, in clam, 

 Mya; B, in cockroach, Periplaneta; C, in lake trout, Triitta lacastris; D, in Fundidus, a 

 stomachless fish. (Modified drawings: A from Yonge,''*' B from Schlottke/™ C and D 

 from Vonk."') 



cellular digestion. In crustaceans such as crayfish they liberate digestive 

 enzymes and are also areas of active absorption. Finally, in such animals as 

 the cephalopods and the chordates, the diverticula are concerned almost 

 exclusively with secretion. 



