INTESTLVAL TEACT OF BIRDS. 



193 



relatively somewhat shorter, the minor expansions of Meckel's tract are less numerous, 

 that bearing Meckel's diverticulum being longer ; there is a supra-duodenal loop ; the 

 cseca are less developed and the rectum is longer. 



Fig. 14. 



Intestinal Tract of a species of Fregata. Lettering as before. 



(5) Pelecanid^. — In the Pelicans {Pelecanus rttfescens, fig. 15) the form of the 

 intestinal tract is simple. The duodenal loop is long, narrow, and some^'hat twisted ; 

 Meckel's tract is nearly symmetrical round the middle mesenteric vein which runs from 

 the position of a large Meckel's diverticulum. There is a well-formed supra-duodenal 

 loop, a suprarcsecal kink drained by the rectal vein, and the caeca are relatively longer 

 than in other Steganopodes. The minor loops of Meckel's tract tend to be bunched up 

 towards the mesenteric vein, a feature that cannot well be represented in a diagium 

 showing the unfolded condition. 



The Steganopodes are typically piscivorous, although some of them also take any kind 

 of floating carrion, and in aU of them allowance must be made for the piscivorous length 

 of gut. Their apocentricity, apart from such homoplasy, consists, as in the Cohonbo- 

 morphge, of a general tendency for Meckel's tract to be expanded into a series of short 

 straight loops. In the Colymbomorphse, however, these loops frequently increase in 

 length and become reduced in number; in the Steganopodes the tendency is rather for 

 the minor loops to increase in number, and for Meckel's tract to be either bunched up 



