GENERAL ZOOLOGY 



Fig. 16.3. A starfish, Asterias, partially dissected from the aboral surface, to show relation- 

 ships of various internal structures. (Redrawn from W. R. Coe, 1912, Geological and Natural 

 History Survey, State of Connecticut, Bulletin 19.) 



pairs of pyloric caeca; one pair lies in each arm, and a single duct leads 

 from each pair into the pyloric stomach. The pyloric caeca consist of series 

 of sac-like evaginations, extending along a central, tube-like canal. The walls 

 of the sacs contain numerous glandular cells which are the apparent source of 

 powerful digestive enzymes. Interspersed among the glandular elements are 

 other cells, which function in the absorption of products of digestion and in 

 the storage of reserves. All these cells together constitute a single-layered 

 epithelium, like the lining of the intestine in a vertebrate. In the pyloric 

 caeca, however, the cells bear long flagella which maintain a steady circula- 

 tion of fluids within the cavities of the organs. Specifically directed currents 

 sweep digestive juices toward the cardiac stomach, where the enzymes are 



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