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Show 1896.] INTESTINAL TRACT OF BIRDS. 147 resemblance to the Ostrich is heightened by the fact that in Chauna and the Ostrich the rectum, by being thrown into a subsidiary set of folds, departs in a similar way from the common type. The resemblance between Chauna and Rhea is very striking. The Ducks and Geese (fig. 11) display a very definite and simple modification of the ground-type. It consists simply in the elongation of a limited number, generally five, of the primitive irregular loops of the circular loop. In a young Bernicla magellunica, still in its down plumage, the duodenum and the third part of the gut were in the typical condition, but the circular loop was already pulled out into three or four subsidiary loops, of which the longest bore the yolk-duct vestige. In adult Ducks, Geese, and Swans the arrangement differed in no essential respect from the drawing Fig. 11. Cyynus atratus ; intestinal tract, x, short-circuiting vessel divided. (fig. 11). The duodenum was simple. The duodenal vessel received short-circuiting veins from the hinder portion of the circular loop. A striking feature of the minor loops on the front part of the mid-gut is the presence upon them of minor loops. The circular luop had a huge median mesenteric vein, which ran out to the much elongated subsidiary loop bearing the yolk-duct. It gave off three vessels to three expansions of the pioximal part of the circular loop, vessels to a long and short distal expansion, and a vessel to the straight part of the loop along which the caeca were attached. The rectum was straight and in the typical fashion was supplied by a posterior mesenteric vein. FALCONIFORMES. I have not had the opportunity of examining any of the Catharta?. The Accipitres show a marked divergence from the common type. The gut generally is enormously long, especially in the fish-eaters. From the point of view of relation to type, I cannot see that there is anv special relation between the Accipitrine deviation and the J * 10* |
