INTESTINAL TKACT OF BIRDS. 



203 



to this, is usually elongated and may be similarly twisted. The supra-duodenal loop, 

 the cteca, and the rectum are as in Anseranas. The vast majority of Ducks and Geese 

 that I have examined, however different their size and habits, faithfully reproduce this 

 type. The diagram given for Ci/gaus atratus, witli the most trifling alterations, might 

 serve for Anas, Anser, JEx, Chanlelasmns, Berniolu, DciKjrocijgna, Fuligtda, JSesonetta, 

 Tadorna, and doubtless, so constant is tlie type, for many others. Mergus alheUiis, the 

 Smew, presents an interesting variation (fig. 23). The duodenum is unusually wide ; 

 Meckel's tract is thrown into a large number of very short loops at the periphery of an 

 almost circular mesenteric fold, but Meckel's diverticulum lies at the apex of a somewhat 

 longer fold lying in the axis of the system. There is a supra-duodenal loop, but it is not 



Fig. 24. 



Intestinal Tract of Sjtatidn cliipeata. Lettering; as before. 



drained by a " bridging " vein. The colic ci,eca are paired, but practically non-existent, 

 and Beddard (2. p. 459) mentions an instance where one of the two was absolutely non- 

 existent. At first sight this intestinal tract appears more archecentric than that of any 

 of the other Anseriform birds except the Palamedese, but I do not doubt that it is an 

 instance of what I term pseudocentric simplicity. The caeca are obviously degenerate, 

 and in other Mergansers they are longer ; and examination of the first part of Meckel's 

 tract shows that it might have been derived by a fusion of the three first minor loops, 

 these having been more complicated tlian in Cygmis, and more as they are in Spatula 

 (fig. 24). There is a short supra-csecal kink, but it is not supplied by the rectal vein. 

 Spatula clypeala (fig. 24) shows a form of gut which is simply a further elaboration of 



