212 



DE. P. CHALMERS MITCHELL ON THE 



The carnivorous forms are on the average the larger, and the carnivorous shortening 

 of the gut is in consequence disguised by the relative increase in length associated with 

 size. The general features of the group are a tendency for the duodenum to he irregular, 

 enlarged, very long, or spirally twisted ; for Meckel's tract to exhibit three definite minor 

 loops anterior to a median loop bearing a Meckel's diverticulum, and, posteriorly to that, 

 first one or two irregular loops and then a supra-duodenal loop and at least one supra- 

 cjT-cal kink drained by the rectal vein ; the ca3ca are always vestigial and the rectum 

 short and straight. The departures from this common type are first, the irregularities 

 in the fish-eaters ; second, a progressive tendency for the lengthening of Meckel's tract 



Fig. 34. 



Intestinal Tract of Pandion haliaetvg. Lettering as before. 



in the axial line with consequent obliteration of one or more of the other minor loops, 

 and, in the most apocentric cases, with a spiral folding of the tract ; third, Serpentarius 

 shows distad of the first three loops of Meckel's tract a circular expansion of the mesentery 

 bearing a number of minor loops, and this condition leads naturally to the condition in 

 Cathartes, where the circular expansion involves the second and third of the definite 

 loops on the proximal side of Meckel's tract. Attempts have been made to show a more 

 intimate relation between the Cathartae and some of the Ciconiiform birds than between 

 these and other Falconiformes ; there is no ground for such a conclusion in the structure 

 of the intestinal tract. Still less ground is there for attempting to place in intimate 



