204 



DR. P. CHALMERS MITCHELL ON THE 



the Cygnvs type. The modifications are confined to Meckel's tract. The three most 

 anterior minor loops of that region are complicated by an elaborate series of minor 

 folds; the axial loop bearing Meckel's diverticulum is as in Ci/gims, but the loop next 

 posterior to that is enormously long and folded on itself, the vein having left the 

 mesentery and running a much shorter course than the loop itself. In Nettopus 

 coromcmdeliamis (fig. 25) the gut is relatively shorter, and an apocentric simplification 



Fig. 2b. 



Intestinal Tract of Nettopus coromandelianus. Lettering as before. 



has taken place. The three proximal loops of Meckel's tract are represented by one 

 short and then a very long loop, and the loop next distad of the axial loop is contorted. 

 In these modified loops the veins leave tlie mesentery, a condition comparatively rare 

 among birds, but very common in the Anseres. 



Considering them from the point of vievr of the intestinal tract, it is plain that the 

 other Anseriformes must be removed from the Palamedese. The latter are archecentrici 

 The former start from a metacentric position common to the Colymbomorphoe and the 

 Ciconiiformes, but have diverged apocentrically from that position, forming a specially 

 Anserine metacentre (Plate 22). 



