INTESTINAL TKACT OF BIEDS. 201 



ANSERIFORMES. 

 PALAMEDE^E. 



PALAMEDEID^E. I described the intestinal tract of Palamedea above (fig. 1). The 

 intestinal tracts of Chauna chavaria (26. fig. 10) and of C. derbiana do not differ from 

 that of Palamedea in any essential detail. I am following Dr. Gadow's classification for 

 convenience of reference, but it is obvious that from the character of the intestines the 

 PalamedeaB have no claim to be placed in close association with the other Anseriform 

 birds, or indeed with any of the Carinate birds with which I have as yet been dealing. 

 The Palamedese exhibit what I take to be the most primitive or archecentric type of 

 intestinal tract to be found among birds. In the gut they have a general resemblance to 

 the Ratites, and to the lowest members of all the other groups ; to such they bear more 

 resemblance than to the Ducks and Geese, which in the intestinal tract exhibit a definite 

 or uniradial apocentricity, no trace of which occurs in any of the three Screamers. On. 

 the character of the intestinal tract alone I would not remove the Screamers from other 

 birds, but rather all other birds from the Screamers, leaving them in central and 

 primitive isolation. 



AN SERES. 



ANSERID^E. I have shown that in the Carinates 1 have up to this point discussed, 

 with the exception of the Palamedeae, there is strong evidence for the existence of the 

 apocentric type of gut which forms a metacentre from which the various groups have 

 diverged further. The metacentric character consists chiefly in the transformation of 

 Meckel's tract into a definite series of narrow, straight loops, folded in the mode Gadow 

 terms orthocoelous, and arranged nearly symmetrically round the middle mesenteric vein, 

 which forms an axial line running from a Meckel's diverticulum. The form of the gut 

 in the Anserida3 can be referred easily to such a metacentric condition. In Anseranas 

 melanoleuca (fig. 22) this metacentric condition is reproduced with almost diagrammatic 

 fidelity, an interesting circumstance in view of the primitive position among the Anseres 

 generally assigned to this bird. The duodenum is a long narrow loop ; Meckel's tract is 

 thrown into very symmetrically-arranged narrow minor loops, the most peripheral of 

 which bears a large Meckel's diverticulum. Between this and the duodenum there are 

 three minor loops, a number typical of this part of the gufc in the Anseres. The last loop 

 of Meckel's tract is a typical supra-duodenal loop with the usual " bridging " vein from 

 the duodenum, and with the very long caeca closely applied to it. The rectum is not 

 very short but is straight. In Cygnus atratus, the tract of which I have figured in a 

 former paper (26. fig. 11), certain modifications of the type in Anseranas are present. 

 The first three minor loops of Meckel's tract are more complicated, showing a tendency 

 to give off secondary loops. The axial loop, which bears Meckel's diverticulum, is greatly 

 elongated and usually somewhat irregularly folded, with the result that the main vein 

 leaves the mesentery, being shorter than the loop itself. The minor loop, just posterior 



