INTESTINAL TKACT OF BIRDS. 2^ 



ANSERIFORMES. 



P A L A M E D E yE. 



PALAMEDEiDiE. — 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 

 tliat 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 

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

 birds, or indeed with any of the Carinate birds witli 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 tlian to the Ducks and Geese, which in tlie intestinal tract exhibit a definite 

 or uniradial apocoitricity, no trace of which occurs in any of tlie three Screamers. On 

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

 birds, Init rather all other bii-ds from the Screamers, leaving them in centrjil and 

 primitive isolation. 



A N S E R E S. 



Ansemd.^. — I have shown that in the Cavinates I have up to this point discussed, 

 with the exception of the Palamedete, 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 tlie mode Gadow 

 terms orthocoelous, and ari-anged nearly symmetrically round the middle mesenteric vein, 

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

 in the Anseridae can be referred easily to such a metacentric condition. In Aiiscraiias 

 melanoleuca (fig. 22) this metacentric condition is reproduced Avith 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 symmeti-ically-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 gut in tlie Anseres. The last loop 

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

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

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

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

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

 to give off !~econdary 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 



