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Show 152 MR. P. CHALMERS MITCHELL ON THE [Jan. 14, and blood-vessels remains as in Numenius; but the large subsidiary loop, on the distal limb of which lies the yolk-sac vestige, is pulled out into an enormously long narrow loop, which is then rolled up into a spiral. The distal part of the circular loop is very much reduced, although there still remains a small loop in the position occupied by the long caeca of Numenius and giving a vessel to the duodenal vein. The Gulls display a type that is more divergent than Numenius, in that the caeca are reduced. Larus marinus (fig. 17) shows that in other respects they are as primitive as Numenius. The duodenum is a simple loop with the usual vessel. The circular coil of the mid-gut is thrown into a series of irregular loops, which, however, as in the Limicolae, are more developed on the side Larus marinus; intestinal tract, x, short-circuiting vessel divided. anterior to the yolk-sac vestige. This lies in the normal position opposite the end of the median mesenteric vein. The last part of the circular loop forms an extended subsidiary loop supplied by a short-circuiting vein from the duodenal vessel. I have not found instances myself, but Dr. Gadow states that in some Gulls spiral folds occur in the region corresponding to the spiral fold of Scolo-pax. Thus the Gulls and the Limicolae would form a series of divergences from the common type, but in parallel directions. Pterocles (fig. 18) diverges in yet another direction. The extremely primitive character of the gut is obvious at once. The duodenum, the circular loop, and the rectum are all distinct and have the usual veins. The middle of the mid-gut is marked by the vestige of the yolk-sac placed at the end of the median mesenteric vein. As in Charadrhformes generally, the anterior portion |
