ALIMENTARY OANAL 25 



paid to fixed points in the intestine, such as the caeca or the 

 viteUine duct. They express, however, an interesting series 

 of facts. The general term of orthocoelous is appHed to 

 those cases where the folds are as a rule parallel to each 

 other and in the long axis of the body. When they form 

 spirals the general term of cyclocoelous is applied to them 

 by Gadow. 



The prevailing number of loops is four, of which the first, 

 the duodenal (which contains the pancreas), is a loop which 

 rarely undergoes additional twisting. The orthocoelous con- 

 dition may be regarded as the starting point. The cyclo- 

 ccelous arrangement, as will be seen by the figure, is derived 

 from the orthocoelous by the conversion into one spiral of 

 the second and third loops. In ;all the Passeres the cyclo- 

 coelous arrangement is arrived at by a spiral twisting of the 

 middle or second loop only (there being but three loops) ; 

 this kind of gut has been termed by Gadow mesogyrous. 

 The Limicolse, which have a spiral formed by the second and 

 third loops, are also, of course, mesogyrous ; but it is clear that 

 a similar state of affairs has been arrived at independently. 

 Finally, there is the telogyrous condition, in which merely the' 

 end of a given loop or loops becomes twisted into a spiral, 

 the rest remaining straight. This is shown in the last of 

 the series of figures on p. 24. In such cases, as in the one 

 figured, the duodenal loop rarely, but still occasionally, under- 

 goes a twisting. The plagiocoelous condition is an irregular 

 twisting of the. ends or of parts of the loops of an orthocoelous 

 gut. These varied arrangements of the gut may be recog- 

 nised in most birds ; but there are a few exceptions of which 

 note must be taken. In certain fruit-eating birds, such as 

 Carpophaga, Bhamphastos, the gut is so short and wide that 

 the number of loops is reduced, and the arrangement quite 

 undecipherable. On the other hand the extremely lengthened 

 gut of the fish-eating Pandion produces an equal confusion. 



Since Gadow's description of the coils of the intestinal 

 canal in birds the subject has been studied from another point 

 of view by Chalmees Mitchell. > Gadow considers only 



' 'On the Intestinal Tract of Birds,' P. Z. S. 1896, p. 336. 



