INTESTINAL TEACT OF BIRDS. 263 



Swimming-birds and most Waders, but that it disappears very early in Birds of Prey, 

 Parrots, Woodpeckers, and Singing-birds. He regards it as a functionless rudiment. 

 Lonnberg and Jagerskiold (21) examined a large number of birds, chiefly Sea-birds and 

 Waders, for it, not contenting themselves with single individuals, and found it absent in 

 most Gulls and Terns, present in Waders, Ducks, Herons, and some others. As at an 

 early stage in my investigations I found it an important point of morphological orien- 

 tation, I searched for it in each of the very large number of birds upon which this 

 communication is based, and found its presence much more frequent than has been stated. 

 An interesting feature in connection with it is, that in a large number of cases it is sup- 

 ported by a vestige of the primitive ventral mesentery. Usually this appears only as a small 

 fold of tissue tying down the diverticulum to the ventral edge of the gut, but sometimes 

 a strong band runs from this towards the liver, the latter of course being developed in 

 the primitive ventral mesentery. Occasionally when the diverticulum itself was absent, 

 its place was indicated by the presence of a mesenterial vestige, as in many Pigeons. 



I have found the Diverticulum present and large in all the Ratitse ; of the Colytnbiform.es 

 absent only in Podiceps ; present in the Sphenisciformes ; present in the Procellariiformes ; 

 of the Ciconiiformes, present and large in all the Steganopodes but small in Plotus, and 

 present and large in the Ardeidse, Scopidae, Ciconise, and Phoeuicopteri, in many of the 

 Ciconiiformes being very large ; present and large in all the Anseriformes ; present in all 

 the Falconiformes (except a Buteo), and very large in the Falconidte, but usually small 

 in the others ; present and large in the Tinamiformes ; present but usually very small in 

 the Galliformes (except Turnix) ; present and very large in all the Gruiformes, often 

 extremely large, but, as a solitary exception, absent in Heliornis ; present and very large 

 in all the Limicoke; among Lari small and often absent in the Laridse, small, but 

 usually present, in the Alcidse ; present in the Pterocletidae, but usually absent and 

 always extremely small in the Columbidae, a feature in which they stand in marked 

 contrast with the Charadriiformes generally ; of the Cuculiformes, always present 

 although small in the Cuculidse ; absent in the Musophagidae, and probably always 

 absent in the Psittaci ; of the Coraciiformes, always small, but present rather more often 

 than not in the CoruciaB, present and small in most of the Striges, very small but present 

 in most Caprimulgi ; always very small and absent more often than present in the 

 Cypseli, Colii, Trogones, Pici ; of the Passeriformes, absent in the vast majority of cases, 

 when present extremely small except as a solitary case in Menura, where it was very 

 large. In making this review I have excluded those specimens which were marked in 

 my notes as obviously chicks or quite young birds, and the list may be taken as repre- 

 senting with fair exactness the incidence of the diverticulum among the Avian groups. 



In all the c;ises where I have mentioned, in the paragraph above, that Meckel's diverti- 

 culum was small, I think that it was a vestige in the true sense, that is to say a functionless 

 rudiment of an embryonic structure. Sometimes the lumen remained, and contained a 

 few fragments of material resembling yolk, and doubtless remains of the yolk. Rather 

 more frequently the " small " divei ticula had no lumen, and were mere nodular 

 excrescences on the wall of the Tract. Among the cases which I have noted as large there 

 are certainly some (Ratites, Palamedea, etc.) in the same category. The curious feature 



39* 



