THE INTESTINAL TSACT OF BIRDS. 197 



Herons the complexity of the minor loops is very great. The penultimate loop of 

 Meckel's tract is always a typical supra-duodenal loop with "bridging" vein, and then 

 follows a supra-csecal kink. It is typical of the Ardeidse, as is well known, that one of 

 the two colic caBca be absent, and I have found no exception to this, but Beddard has 

 recorded such a case. The rectum itself is straight, but not very short. 



A considerable part of the apocentricity of the intestinal tract in the Ardese must be 

 attributed to the fact that they are relatively large birds with a diet consisting chiefly 

 of fish, in consequence of which the gut is very long and narrow. Underlying this is a 

 general resemblance to the ground-form of the Steganopod and Colymbomorph gut, 

 shown in the symmetry of Meckel's tract around the middle mesenteric vein, the 

 persistence of a large Meckel's diverticulum opposite the end of this vein, and the 

 formation of a kink immediately above the colic caeca but supplied by the rectal vein. 

 The special Ardeine features are the elongation of the duodenum as a narrow fold curving 

 to the left ; the throwing out of Meckel's tract into minor loops, which, straight in the 

 simpler forms and always folded over simply (" orthocoely " of Gadow), tend to become 

 complicated in themselves. The persistence of only one of the colic ca3ca is a most 

 peculiar feature, normally absent only in Scopus. But the absence occurs not infre- 

 quently as an individual abnormality in some other birds, and I shall make further 

 reference to such cases. 



Although Scopus, so far as the character of the intestinal tract takes us, is more 

 archecentric than the Herons and Bitterns, it plainly belongs to their group rather than 

 to the Storks and Ibises. 



C ICONIC. 



(1) CICONIID.E. The Storks, of which I have examined a considerable number, present 

 a most interesting series of modifications. Anastomus oscitans (see Plate 21), the Indian 

 Open-bill, displays so little difference from the ground- form of the intestinal tract among 

 the set of birds I have been discussing, that I do not think it necessary to figure it in a 

 separate block. The duodenum is short and straight ; Meckel's tract is thrown into a 

 very large number of short straight loops nearly symmetrically disposed around 

 the middle mesenteric vein, the latter running backwards from a large Meckel's 

 diverticulum. There is a very large and complicated supra-duodenal loop, more compli- 

 cated than in any of the other Storks I have examined, but drained by the usual bridging 

 vein. Above the reduced cseca lies a short kink drained by the rectal vein, and the 

 rectum is straight and of moderate length. In Pseudotantalus ibis (fig. 19) the typical 

 Ciconiine apocentricity begins to appear, and this is of the definite type that I call 

 uniradial and am. inclined to regard as a sure sign of affinity. The duodenum is 

 enormously long, but the bending which appeared in Herons is here transformed to a 

 spiral twist, represented in the figure as partially uncoiled, with the result that the vein 

 is out of the mesentery. The first minor loop of Meckel's tract is very large and is in 

 itself slightly twisted, and, in the unfolded state, partly rolled in the duodenal spiral. 

 The remaining portion of Meckel's tract consists of a few simple folds, symmetrical 



SECOND SERIES. ZOOLOGY, VOL. VIII. 31 



