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154 MR. P. CHALMERS MITCHELL ON THE [Jan. 14, gut as a simple derivative of the type seen in Pterocles. The duodenum is longer and narrower. The circular loop is enormously expanded, but the three subsidiary loops seen in Pterocles remain. The first of these is somewhat shortened ; the second, that bearing the yolk-sac vestige at its end, is enormously lengthened ; the mesentery is folded along the line of the median mesenteric vessel, so that the two limbs of the loop are brought in contact with each other, and, finally, the whole folded loop is rolled into a rough spiral. The third subsidiary loop of the circular part of the gut has the same arrangement and veins as in Pterocles; but the caeca no longer run along it, but occur as very short stumps upon the rectum. CPCULIFORMES. Of these, I have examined only Corythaix (chlorochlamys and persa) and a number of Psittaci. So far as I can see, one has to go back to the common type for both. Corythaix (fig. 20) has a remarkably short and wide gut, in correspondence with its frugi- Fig. 20. Corythaix chlorochlamys ; intestinal tract, x, short-circuiting vessel divided. vorous habits. The duodenal loop is wide and straight. The circular loop is short; its anterior portion forms a normal coil, is slung at the circumference of the circular mesentery, and is supplied by radiating branches of the median mesenteric vein. N o doubt the vestige of the yolk-duct occurs upon this; but in m y specimens, which were all affected with tubercular nodules on the gut, I failed to identify it. The distal portion of the circular cod, along which the caeca run in the primitive type, is pulled out into a narrow subsidiary loop, the distal portion of which gives a short-circuiting vein to the duodenal vein. The rectum is straight, and there was no trace of caeca. The gut appears to be directly derived from the primitive type by shortening and by loss of the caeca, the distal |
