210 



DK. P. CHALMERS MITCHELL ON THE 



of the system carrying a Meckel's diverticulum. There is a well-formed supra-duodenal 

 loop, which is spirally twisted, and a large supra-caecal kink has a similar arrangement- 

 The caeca are vestigial, and the rectum is short and straight. Haliaetus leucogaster 

 differs from the foregoing only in that its duodenum is spirally twisted. These two 

 birds are large and chiefly piscivorous, and the homoplastic increase in gut-length has 

 obscured the peculiar characters of the Falconiform gut, but the general symmetry, the 

 peculiar duodenums, and the well-formed supra-caecal kinks are sufficiently distinctive. 

 The other Aquilinae repeat exactly the pattern displayed by Circus, the only slight 

 modification I have found being that the supra-duodenal loop in Spizaetus, although 

 drained by a " bridging " vein, is very small. The supra-csecal kink is very large in 

 most and distinct in all. 



(5) Buteonince. Of these I have examined Astur tachiro, Asturiiia magnirostris, 

 Buteo erythronotus, B.ferox, B.jacal, Milvus govinda, M. ictinus, M. migrans. In all 

 the pattern of Circus is reproduced with close fidelity. The duodenum is irregular, 

 sometimes long, narrow, and straight as in the genus Buteo, sometimes irregularly 

 expanded, or folded upon itself several times as in some species of Milvus. Meckel's 

 tract is always as in Circus, save that in a Buteo no trace of Meckel's diverticulum was 

 retained. The supra-duodenal fold is always present as also is a large supra-caecal kink. 

 The caeca are vestigial and the rectum is short and straight. 



(6) Falconince. I have examined Falco concolor, F. Feldeggi, F. lanarius, F. mela- 

 nogenys, F. peregrinus, and Microhierax melanoleucus. The Falconinae certainly exhibit 



Fig. 32. 



m 



Intestinal Tract of Falco melanogenys. 

 .i., visceral nerve-chain. Lettering as before. 



the most specialized or apocentric form of gut among the Falconida3. The duodenum is 

 always a large irregular loop, sometimes with minor folds (fig. 32), sometimes bent on 

 itself (fig. 33). Meckel's tract is always very much elongated in the axial line, and 



