188 DE. P. CHALMEKS MITCHELL ON THE 



into minor systems. Of these, two are well-marked in all : a very large loop towards 

 the distal extremity of Meckel's tract and drained by a factor of the middle mesenteric 

 vein, and a long narrow supra-duodenal loop which is drained by a " bridging " factor of 

 the duodenal vein. In Spheniscus the portion between the supra-duodenal loop and the 

 rectum, which is very long in all, is expanded into a minor fold, an arrangement 

 characteristic of the Eagles, and to which I give the name " supra-cseeal kink." The 

 rectum in all is extremely short, and the caeca are vestigial in those that 1 have 

 examined, but Gadow mentions that they were relatively long in a Eudyptes. 



It is plain that the character of the tract in the Sphenisciformes is markedly 

 apocentric. When due allowance has been made for the piscivorous lengthening, the 

 form still remains apocentric : the short caeca, the tendency to form minor loops, the 

 supra-duodenal loop, the tendency to form a supra-caecal kink, and the extremely short 

 rectum make up a peculiar and distinct type. 



PROCELLARIIEORMES. 



Of these I have had an opportunity of examining only the Northern Petrel and the 

 Albatross. In Fulmarus glacialis (26. fig. 7) the duodenum is compound, and Meckel's 

 tract is expanded into six very long, narrow and straight minor loops, the fourth of 

 which bears Meckel's diverticulum, while the last is a distinct supra-duodenal loop 

 drained by a " bridging " vein. The terminal portion of Meckel's tract is long, thrown 

 into supra-ceecal kinks as in Sphenisctis and the Eagles, and is drained by the posterior 

 mesenteric vein. The caeca are vestigial, and the rectum is extremely short. In 

 the Albatross, Diomedea exulam (fig. 9), the duodenum is simple, and Meckel's tract is 

 drawn out into a series of extremely long narrow loops (the length of these is under- 

 estimated in the figure). The form of the tract is much alike in the Albatross and the 

 Petrel ; the chief difference is that the first three minor loops of the Petrel are repre- 

 sented in the Albatross by two long loops with shorter loops between them. A very 

 long loop bearing the Meckel's diverticulum then follows in both ; the lower portion 

 of Meckel's tract, the supra-caecal kinks drained by the rectal vein, the vestigial caeca, 

 and the very short rectum are alike in each. The only striking difference is that 

 there does not appear to be a definite supra-duodenal loop with " bridging " vein in 

 Diomedea. The specimen I examined had been preserved for long in spirit, and 

 possibly I may have overlooked a "bridging" vein, although I examined the region 

 minutely for it. 



It is plain that the Procellariiform birds present a markedly apocentric type of intes- 

 tinal tract, the special characters being the transformation of the middle loop into a 

 number of definitely-placed minor loops, the appearance of supra-csecal kinks on the 

 large posterior portion of Meckel's tract, drained by the rectal vein, the vestigial caeca, 

 and the very short rectum. 



Gadow (12) unites the Colymbiformes, Sphenisciformes, Procellariiformes, and extinct 

 Ichthyornithes into a " Legion " under the name Colymbomorpb.se. Concerning the 

 intestinal tract of the extinct forms we have no information. The others have all moved 

 out from the archecentric condition. Their apocentricity is first a relatively increased 



