INTESTINAL TRACT OF BIEDS. 239 



been made, the various conformatioBs exhibited by the dififerent genera of both families 

 (from the point of view of conformation of the gut no distinction can be made between 

 the families) appear obviously to belong to the simpler RaUine and Charadriiform 

 patterns. The only other possible suggestion of affinity is provided by the existence of 

 the supra-caecal kinks in some Gulls and Hawks ; but, as the other portions of the gut 

 are so unlike the conformations found among the Pelargo-Colymbomorphine assemblage, 

 I think the presence of the kinks in these few forms must be taken as a multiradial 

 modification. 



Pleroclo' Columbine Assemblage. 



Pterocles. — I have already described and figured the gut in Ptentcles blcmstins (26. 

 fig. 19). The duodenum is straight and rather narrow. Meckel's tract is expanded to 

 form three definite loops. The first of these is long, expanded at its apex, and curiously 

 bent on itself. The second is an axial loop bearing Meckel's diverticulum at its apex. 

 The third is a deSnite supra-duodenal loop, drained by a '" bridging " vein and having 

 the long caeca closely applied to it. The rectum is short and straight. In Plerocles 

 alchata the condition is exactly similar, except that the caeca are relatively longer. 



C L r M B .£. 



I have examined a large number of Columbidse, including the genera Calcenas, 

 Chalcopelia, Chalcophaps, Columba (many species and varieties!, Columbula, Geopelia, 

 Goura, Leucosarcia, Ocyphajjs, CEna, Fhops, Phlogcenas, Ptiloptis, Stanifjenas, Trei'on, 

 and Turtur. The conformation of the gut is best understood by taking it as a simple 

 but more apocentric derivative of the condition in Pterocles. The duodenum is a 

 simple loop. Meckel's tract is thrown into the same three folds. The first is simpler 

 than in Pterocles. The second or axial loop is usually very much longer, and it may be 

 twisted into an elaborate spiral (26. fig. 19j, and as in Pterocles bears the diverticulum, 

 or a very small vestige of it marked by a ventral mesentery, or no vestige at all. 

 The third loop is a definite supra-duodenal loop very closely modelled on the duodenum 

 and diained by a "bridging' vein. The caeca are always vestigial and not infrequently 

 are absent. Beddard (2. p. 308) mentions that in an example of Tympanistria btcolor 

 only one vestige was present. I have found similar variations not infrequently in the 

 varieties of the genus Columba. but apparently only as individual variations. The rectum 

 is alwavs verv short and straisht. 



There is little difference in the conformation of the gut in the different genera and 

 species. Tlie larser forms in most cases have the length of gut relatively greatly 

 increased, and the increase is most noticeable in the spirally twisted axial loop. In 

 some small forms, such as (Ena, the gut is absolutely and relatively shorter, and there 

 is little trace of the spiral. Precisely a similar state of affairs exists among Passerines, 

 where size is one of the chief factors in determining the length of the whole gut, and the 

 consequent elaboration of the axial spiral. In Pliloptis and other fruit-eating Pigeons 

 the whole gut is extremely reduced in length and is very wide. In sucii cases the 

 relation of the pattern to that in ordinary Pigeons can only be guessed. 



36* 



