INTESTINAL TRACT OF BIRDS. 



229 



the three loops "«," "6," and " c " very definitely drawu out. In II. surlnumciisis, the 

 coni'ormation is similar, although the loojis are not so indepcndoTit. In neither is thei'e 

 a diverticulum present. The jiosterior portion of Meckel's tract is a definite supra- 

 duodenal loop drained by two " bridging " vessels. The caeca are of modci-ate length, and 

 the rectum is as in the others. 



It is plain that what I term a metacentral condition underlies the conformation of the 

 alimentary tract in the Gruiform asscmlilage. This mctacentre possesses a simple 

 duodenum ; Meckel's tract is produced into four straight loops, of which " h" the axial 



Fig. 48. 



Intestinal Tract of Heliornis fuliai . Lottoring as in fig. 41. 



loop, carries the diverticulum on its distal liml), and of which the last is a large supra- 

 duodenal loop drained by bridging vessels and with the long caeca closely attached to it. 

 The Rallidaj and Gruidae display this metacentral cliaracter without modification of any 

 important kind. The Dicholophidte and the Otididae have moved apocentrically from it 

 by reduction of loops " a " and " c " and greater specialization of the supra-duodenal 

 loop. Helioniis is metacentral. llhhtochetus and Eurypy(ja are slightly modified, the 

 apparent archecentricity of the latter being possibly pseudocentric. 



SECOND SERIES. — ZOOLO&Y, VOL. VIII. 35 



