244 CHORDATE ANATOMY 



History of the Pancreas. The pancreas seems to be an emergent trait 

 of vertebrates, since no comparable structure is found in the invertebrates 

 or even in the lower chordates. In cyclostomes, the pancreatic tissue 

 remains buried in the substance of the Uver or in the wall of the small 

 intestine. Since no duct appears in these forms, it is assumed that 

 the pancreas was primarily endocrinal and not digestive. Other verte- 

 brates, beginning with the elasmobranchs, have both dorsal and ventral 

 pancreases. 



