18S9.] 



CONVOLUTIONS IN BIRDS. 



305 



dorsally, consequently its ascending branch runs side by side with 

 that of the 3rd. 



III. Playioccelous. — The 2nd loop always, often more loo[)S, 

 are doubled up or turned over with the apices like a horseshoe, 

 giving the loop, which is generally open, an irregular or convoluted 

 ajjpearance. 



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. Oyclocoelous formation by tlie conversion of the second and third 

 loo|)S into one left-handed spiral. Such a conversion of the second 



Jir 



OL 



Diagrammatic representation of the principal relative positions of tUe 

 intestinal loops when seen from the right side. 



a. Isocoelous. h. Antiucelous. c. Anti-Periccelous. d. Iso-Pericoelous. 

 e. Cyclocoelous. /, (j. Plagioccelous. h. Telogyrous. 



The descending branches of the loops are marked by black lines, the ascend- 

 ing or returning branches are dotted. 



The first and third loops in fig. h 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 Limicolse, Laridse, 

 and Columbse. Each of these famihes 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 coucentratiou of two 



