220 



UK. P. CHALMEES MITCHELL ON THE 



large caeca are closely applied, and are drained partly by the recurrent vein and partly 

 by a " bridging " vein. The rectum is relatively short and straight. 



In the G-alli generally the only homoplastic cause of apocentricity that has to be 

 allowed for is the increased length in the larger forms, and this is not sufficiently great 

 to distort the morphological pattern of the intestinal coils. In all, the general character 

 is markedly archecentric ; in the Megapodidse the archecentricity is most definite. In 

 the Cracidae there is an apocentric modification of a definite nature, although not great, 

 and consisting in the peculiar expansion of the distal region of Meckel's tract with 



Fig. 40. 



Intestinal Tract of Pavo cristatv*. Lettering as before. 



coincident alteration of the visceral uerve and of the factors of the middle mesenteric 

 vein. In the Gallidae a similar change has occurred, but has affected the blood-vessels 

 and the visceral nerve (the course of the latter, not indicated in the figure, very closely 

 resembles that in Talegallus) to a much smaller amount. On the other hand, the caeca 

 in the Gallidae are much larger, and the small factor of the duodenal vein, which in Grax 

 runs from them within the mesentery, is enlarged in the Gallidae and has broken through 

 the mesentery. It is plain that, so far as the conformation of the intestine indicates, the 

 Galli are all closely allied, but there is a distinct basis for their division into Megapodidaa, 

 Cracidae, and Gallidae. 



OPISTHOCOMI. 



I have already described and figured the intestinal tract of Opisthocomm cristatus 

 (27. fig. 1). The duodenal loop is short and wide. Meckel's tract is thrown into three 

 well-marked narrow loops, the second of which is rather wider and has a tendency to be 

 twisted into a very slight spiral. In a chick and in two adults I found no trace of 



