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Show 18S9.] CONVOLUTIONS IN BIRDS. 305 dorsally, consequently its ascending branch runs side by side with that of the 3rd. III. Plagioccelous.-The 2nd loop always, often more loops, are doubled up or turned over with the apices like a horseshoe, giving the loop, which is generally open, an irregular or convoluted appearance. IV. Periccelous.-The 2nd loop is left-handed, open, and encloses the 3rd, which is generally straight and closed. This formation is of especial interest, because it leads quite gradually to the V. Cyclocailous formation by the conversion of the second and third loops into one left-handed spiral. Such a conversion of the second Diagrammatic representation of the principal relative positions of the intestinal loops when seen from the right side. a. Isoccelous. b. Anticcelous. c. Anti-Pericoelous. d. Iso-Periccelous. e. Cycloccelous. /, g. Plagioccelous. h. Telogyrous. The descending branches of the loops are marked by black lines, the ascending or returning branches are dotted. The first and third loops in fig. b are "right-handed," the second is "left-handed ; " in fig. c the second is "left-," the third " right-handed," &c. and third loops into a spiral has taken place in the Limicolae, Laridee, and Columbae. Each of these families possesses some genera in which the spiral is still represented by long, oval, concentric turns, and even some genera which still exhibit the periccelous type with the two loops in question still separate, distinct, and more or less straight. Not every spiral, however, is formed by the concentration of two |