198 



DE. P. CHALMEES MITCHELL ON THE 



about the middle mesenteric vein, which runs from a Meckel's diverticulum. The distal 

 portion of Meckel's tract forms first a distinct but short supra- duodenal loop, and 

 then a double kink drained by the rectal vein. The caeca are reduced and the rectum 

 is straight and short. Dissura episcopus, Leptoptilus crumeniferus, L. argala, and Ciconia 

 alba are practically identical with this condition. In Ciconia nigra, which I have already 

 figured (26. fig. 9), the condition is similar, except that the duodenal loop and the first 



Fig. 19. 



m... 



Intestinal Tract of Psewdotantalus ibis. Lettering as before. 



loop of Meckel's tract form more perfect spirals, which in the unfolded condition are 

 rolled together. In Mycteria americana (fig. 20) a similar condition exists, but the 

 duodenal spiral and the spiral on the first loop of Meckel's tract are still longer and 

 more complex, and are more intimately rolled together, with the result that certain 

 factors of the duodenal vein run across draining the loop with which the duodenum is 

 associated. These are represented in the figure as divided and the spirals are partly 

 untwisted. Among the Storks, then, we see the interesting state of affairs that the 

 character of the gut, starting from a metacentric position common to a large group of 

 birds, develops along a special radius forming a uniradial line of apocentricity. 



