660 DR. p. CHALMERS MITCHELL ON THE 



Examination of the preparation of the caecum in the College of 

 Surgeons' Museum, which Forbes had seen, as cited by Beddard 

 in a footnote, made it most probable that that was the portion of 

 the intestinal tract removed from the specimen Beddard examined. 

 There is therefore no evidence in favour of Dr. Beddard's 

 suggestion that the ctecuni in Bcdceniceps may be absent, or so 

 small as to be unnoticed,. 



The large intestine from the c?ecum to the cloaca is relatively 

 long in Bcdcenice'j)s and is rather wider in calibre than the small 

 intestine ; it is thrown into a series of short irregular loops, 

 threaded, so to say, on a mesentery which is much shorter than 

 the course of the gut itself, and which in the usual way is drained 

 by a large branch of mesenteric vein. 



I have shown on a former occasion (30) that the characters 

 of the intestinal tract are capable of affording a large amount 

 of information as to the inter-relationships of the groups of 

 birds. The primitive gut may be regarded as a tube not much 

 longer than the length of the body-cavity it traverses and 

 suspended from the dorsal body-wall by an antero-posterior 

 mesentery. It is fixed at its anterior end, where it joins the 

 stomach, at its posterior end, where it enters the cloaca, and near 

 the middle of its length, on its ventral surface, where it is con- 

 tinuous with the yolk-sac. The great embryonic vein forms the 

 chief radius of this crescentic loop, running up to the dorsal wall 

 from the yolk-sac, and receiving a large tributary, which runs 

 parallel with the dorsal wall, from the hind end of the body. In 

 the course of growth the gut becomes much longer than the 

 distance separating its anterior and posterior fixed parts, and the 

 lengthening takes place by the outgrowth of subsidiary loops from 

 the primitive gut. The position of these loops with regard to the 

 fixed points of the gut, and their rlumber and character, difi'er in 

 different cases, with the result that when the alimentary tracts 

 are laid out on the dissecting board in the fashion in which I have 

 described, they form definite patterns. In their main features, 

 these are constant in individuals of the same species, closely 

 similar in the species of a genus, and show definite relationships 

 in the families and greater groups. A type of pattern persists 

 thi'ough the large divisions and shows a gradual increase in 

 defiiiiteness and specialization in the difierent members of these 

 groups, with the result that the patterns can be arranged in 

 family trees. These correspond so closely with information that 

 can be derived from other anatomical characters, that I regard 

 them as being an extremel}^ useful guide to the relationships of 

 birds. Obviously patterns are more easy to place in the system 

 when they are highly specialized and complex, but even the 

 shortened guts of fi'uit-eaters may retain marked indications of 

 pattei'n. 



In the great assemblage of birds which Gadow (16) has 

 called the Pelargomorphine Legion, in which Balcenice'ps must 

 certainly be placed, the pattern of the gvit is relatively complex. 



