ANATOMY OF THE SHOE-BILL. 663 



my memoir. He also thinks that I do not distinguish sufficiently 

 between what he terms " fixed loops definitely formed by a narrow 

 mesentery, and the irreg'ular folds into which any mobile coil of 

 the intestine may fall when disposed on the dissecting board." 

 The whole tract is of course supported by mesentery, and 

 Dr. Beddard's " fixed loops " and irregular folds are merely the 

 beginning and final result of differentiation. The loops to which 

 I have called attention are fixed by their morphological position, 

 and they may be wide or narrow, long or short. More serious, 

 however, is Di-. Beddard's misapprehension of the morphology of 

 the gut which leads him into very curious comparisons. He 

 states " that there are no essential differences between the 

 intestinal tract in Birds and Crocodiles." He accepts as "per- 

 fectly correct " a diagram I gave (26, p. 137) of the alimentary 

 tract in the Alligator, in which the canal is displayed as showing 

 a series of almost exactly similar loops from the stomach to 

 the cloaca, suspended on a crescentic fold of mesentery. As 

 the pancreas lies in the first of these loops, the latter may by 

 analogy be called the duodenum, but it is simply the first of a set 

 of regular loops. MeckeFs tract and the delimitation between 

 that and the large intestine are not shown ; it is quite clear that 

 Meckel's tract is not differentiated. Comparison with the next 

 figure, that of the tract in an embryonic pheasant, shows the 

 essential difference. Immediately posterior to the duodenum a 

 mesenteric area, corresponding to a very shoi't length of the whole 

 distance from the stomach to the cloaca, grows out into an 

 enormous nearly circular tract, of which the great vein from the 

 yolk-sac forms nearly a diameter. This region is Meckel's tract, 

 and from the point where it returns to the dorsal line again and 

 where the. ca^ca, if present, are given off, the large intestine 

 begins, and corresponds to a much larger part of the primitive 

 distance from the pyloric extremity of the stomach to the cloaca., 

 than the combined length of origin of the duodenum and Meckel's 

 tract. This mode of development of the gut dominates its adult 

 morphology. So also Dr. Beddard does not appreciate the mor- 

 phological importance of the position of Meckel's diverticulum, 

 the remnant of the yolk-sac. Fortunately it persists throughout 

 life in most of the different groups, and its presence rules out 

 such comparisons as Dr. Beddard makes between particular 

 loops in Rhea and a Tinamu (with a Passerine intervening in 

 the argument !). He is trying to identify different morphological 

 material, belonging to different somites of the embryo, and this 

 error makes his conclusions invalid. It would be of great interest 

 to examine young chicks of those birds in which the rudiment of 

 the yolk-sac does not usually persist, and this would clear up some 

 of my dubious cases. But so far as they go, the gut-patterns afford 

 an amazingly conclusive body of evidence as to the Avian system. 

 Cloaca. — The rectal portion of the large intestine expands 

 suddenly to enter the large cloaca. The first chamber of the 

 cloaca, called the coprodpeum by Gadow, is separated by a thin 



