216 DR. P. CHALMERS MITCHELL ON THE 



represented in figure 36 was present in two specimens of Rhynchotus, absent in another, 

 and present in Nothura. The caeca were long in all, and Beddard (2) has notified the 

 presence of long caeca in the other genera and species, and of very peculiar caeca in 

 Calodromas. The rectum, is short and straight. 



The figure may be taken as representing the morphological character of the Tract in 

 the Tinamus, as there is little correction to be made for habits, and as the conformation 

 is practically identical in relatively large forms such as Rhyncliotus, and relatively small 

 forms such as Nothura. It is clear, then, that the type of the intestinal tract in the 

 Tinamiformes is markedly apocentric, and differs from the archecentric type of Pala- 

 medea and of the Strutkious birds in that the rectum is straight, and more notably in 

 that Meckel's tract is expanded into two long, straight, and narrow loops, one anterior, 

 the other posterior to the rudiment of the yolk-sac, both being orthocrelous. Naturally, 

 as the Ratites have intestinal tracts of archecentric conformation, it is as possible that 

 the Tinamiform gut may be derived from the Ratite gut as from that of any other 

 archecentric form. But so far as the character of the intestinal tract goes, there is no 

 reason to associate the Tinamus specially with the Ratites. Nor is there any reason 

 to associate the Tinamus in this matter with the Gralliform.es, for in these the gut 

 shows a fundamental archecentricity underlying a tendency to apocentric development 

 in the direction of expansion of that part of Meckel's tract supplied by the recurrent 

 branch of the middle mesenteric vein, and there is no trace of this feature in the Tinamus. 

 The gut of the Tinamus bears a close resemblance to that of specialized Ralline forms 

 such as Otis (fig. 45). The gut of Otis, as I shall show later, can be regarded without 

 difficulty as an apocentric derivative of that of less specialized Ralline forms, and for 

 this reason the resemblance between it and the Tinamu may be merely superficial. 

 There is, however, another reason for not rejecting the Ralline affinities of the Tina- 

 miform gut too readily. As I shall explain later, I have only gone a little way in study 

 of the autonomic nervous system, and therefore cannot yet weigh the value of evidence 

 to be drawn from the modifications exhibited in different birds. There are, however, at 

 least two strongly contrasting types. In one of these the visceral nerve of Meckel's 

 tract forms a ganglionated chain which follows the contour of the gut. This type 

 occurs in Palamedea (fig. 1, v.n.}, in the Struthious birds, and in the GJ-alliformes. In 

 the other type there are a much smaller number of larger ganglia on the visceral nerve 

 (Otis, fig. 45, v.n.). This type occurs in some of the Ralline birds and in at least 

 Nothura. Another striking resemblance is that between the conformation of the gut 

 in the Tinamus and in Opisthocomus. To this I shall recur later. The conformation 

 of the gut, then, supports those who, like Gadow, isolate the Tinamus as Tinamiformes, 

 but at the same time suggests possible relationships with Gfruiform birds and with 

 Opisthocomm. 



GALLIFORMES. 



MESITES. I have no information regarding this group. Naturally knowledge of the 

 conformation of the alimentary tract is much to be desired in the case of a bird the 

 affinities of which are doubtful. 



