188 DR. p. CHALMERS MITCHELL OX 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 Sjifieaiscits the portion between the supra-duodenal loop and the 

 rectum, wliich 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-csecal 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 Eiidyptes. 



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

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

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

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

 rectum make up a peculiar and distinct type. 



peocellaeiifor:mes. 



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

 Albatross. In Ftdmarus glacialis (26. fig. 7) the duodenum is compound, and ileckel'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 

 di-ained by a "bridging" vem. The terminal portion of Meckel's tract is long, thrown 

 into sxipra-Cfecal kinks as in Spheniscu.^ and the Eagles, and is drained by the posterior 

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

 the Albatross, Diomedea exulans (fig. 9), the duodenum is simple, and ^reckel's tract is 

 drawn out into a series of extremely long nan'ow 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 difterence is that the fii-st 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 divei-ticulum then follows in both ; the lower portion 

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

 and the verv short rectum are alike in each. The onlv striking ditference 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 1 may have overlooked a ••bridsins" vein. althoiis:h I examined the resrion 

 minutely for it. 



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

 tinal tract, the special charactei"S being the transformation of the middle loop into a 

 number of definitely -placed minor loops, the appearance of supra-c<ecal kinks on the 

 large posterior portion of Meckel's tract, drained by the rectal vein, the vestigicd caecei, 

 and the very shon rectum. 



Gtidow ^12) vuiites the Colymbiformes, Sphenisciformes, Procellariiformes, and extinct 

 Ichthyornithes into a '"Legion" under the name Colymbomorphce. Concemin? the 

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

 out from the archecentric condition. Their apocentricity is fii'st a relatively increased 



