INTESTINAL TRACT OF BIEDS. 



229 



the three loops " a" " b," and " c " very definitely drawn out. In H. surinamensis, the 

 conformation is similar, although the loops are not so independent. In neither is there 

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

 duodenal loop drained by two " bridging " vessels. The caeca are of moderate 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 assemblage. This metacentre possesses a simple 

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



Fig. 48. 



Intestinal Tract of Heliornis fulica. Lettering as in fig. 41. 



loop, carries the diverticulum on its distal limb, 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 Rallidse and Gruidse display this metacentral character without modification of any 

 important kind. The Dicholophidse and the Otididse have moved apocentrically from it 

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

 loop. Heliornis is metacentral. RMnochetus and Eurypyga are slightly modified, the 

 apparent archecentricity of the latter being possibly pseudocentric. 



SECOND SERIES. ZOOLOGY, VOL. VIII. 



35 



