214 



DE. P. CHALMEES MITCHELL ON THE 



common. Platalea is less apocentric than the Steganopod metacentre. In it Meckel's 

 tract cliflFers from that in the Pelargo-Colyrahomorphine metacentre only in that it is 

 elongated, thrown into many short folds, and sjiirally twisted as a whole. Phcenicopterus 

 is like Platalea, but it is still more archecentric, inasmuch as its caeca are functional. 

 The Falconiformes have developed from the Steganopod metacentre so as to display a 

 central type of their own, characterized by an elongation of Meckel's tract, in the line 

 of the axial loop, the latter bearing the diverticulum, and the settling down of the gut 



Falco 



Fig. 35, 



Ciconine Types Falconing Vulturid^ 



Polyborin^ 

 Buteomnffi 



Procelkriifornies 



Sphenisci 



Podicipedes 



\ 



Colymjbi 



Gypohierax CatJiarLe? 

 Serpentarius 



Spatula 



Pelargo- 



Colymbimorphme 



Metacentre 



Mergus 



Archecentric Types 



Palamedea 



Ratitas 



Evolution of Intestinal Tract in the Pelargo-Colymbomorpliine Brigade. 

 (For Colymbimorphine read Colymbomorphine.) 



between this and the duodenum into three definitely formed loops. From this the higher 

 Falconidse move apocentrically, the axial loop of Meckel's tract increasing in length at 

 the expense of the others and being twisted into a spiral. Gi/pohierax, with its irregular 

 minor loops on Meckel's tract and its two supra-caecal kinks, leads to the Vulturidae. 

 Serpentarius with its spherically expanded Meckel's tract arises somewhat outside the 

 Falconiform metacentre, and may well lead to the more apocentric Cathartoe, which have 



