214 



DE. P. CHALMERS MITCHELL ON THE 



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

 tract differs from that in the Pelargo-Colymbomorphine metacentre only in that it is 

 elongated, thrown into many short folds, and spirally 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 Falcqninag Vulturida? 



Polybonn.! 

 Buteoninffi 



Ardeidas 



Procellariiformes 



Accipitrina 

 Aguilinae 



Gypphierax Catharte? 



\ x > - Serpentarius 



Falconiform 

 Metacentre 



Anastomus 

 Scopus 



Sphenisci 



Podicipedes 



Colymbi 



Spatula 



Nettopus 



Steganopod 

 Metacentre 



' Pelargo- 

 Colymbimorphine 

 Metacentre 



Anserine 

 Metacentre 



Platalea 



Phcenicopterus / 



Anseranas 



Mergus 



Archecentric Types 



Palamedea 



Ratitae 



Evolution of Intestinal Tract in the Pelargo-Colymbomorphine Brigade. 

 (For Colymbimorphine read Colymbomorphine.) 



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

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

 the expense of the others and being twisted into a spiral. G-ypohierax, with its irregular 

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

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

 Ealconif orm metacentre, and may well lead to the more apocentric Cathartse, which have 



