238 



DB. P. CHALMEES MITCHELL OX THE 



unidentified, as the diverticulum is not present, and there is a highly specialized supra- 

 duodenal loop left free hy the degeneration of the caeca and closely rcsemhliiig the 

 duodenum in shape. This similar moulding of the duodenum and the supra-duodenal 

 loop is a condition found in many of the higher forms Avith relatively short guts. 



Alcid^. — In Fratercida arctica (fig. 57) a conformation of the same general character 

 as that in many of the Gulls appears. The duodenum is of moderate size and not 

 twisted. The greater part of IMeckel's tract consists of a set of sliort loops, the axial 

 of which bears a large diverticulum in the Ralline position, and of a very large supra- 



Fis. 58. 



ln(os(in;il Tract of Loinriit troilc. Lettering as before. 



duodenal loop from which there has not been separated loop " c." Above the vestigial 

 caeca is the curious supra-cjecal kink to which attention was di*awn in certain Gulls. 

 In Lomvia iro'de (fig. 58) a Gull-like pattern is displayed. There is no diverticulum to 

 jjulicatc the exact topography. There is a well-formed supra-duodenal loop and a large 

 supra-oa>cal kink. The caeca are vestigial, and the rectum is extremely short. 



The Larida^ and Alcidte are families of birds typically lish-eating, and in which 

 lengthening and narrowing of the gut has to be allo^^ (>d for. That alloAvance having 



