INTESTINAL TEACT OF BIEDS. 



237 



larger. However, the most striking circumstance is the appearance above the caeca in 

 the posterior part of Meckel's tract of a set of kinks drained by the rectal vein. In the 

 drawing, the relative importance of these has been slightly exaggerated ; but I was 

 anxious to call attention to them, as their presence suggests either an unlikely affinity 

 between the Laridso (and the Alcidse) and the Pelargo-Colymbomorphine assemblage, or, 

 more probably, that the existence of this kink is a multiradial apocentricity to which too 

 much importance must not be attached. In Stercorarius crepidatus (fig. 55, p. 235) a 



Fig. 57. 



Intestinal Tract of Fratercula arctica. Lettering as in fig. 41. 



more archecentric type of gut is displayed, the arrangement rather closely resembling 

 that found in Thinocorys and Glareola. The duodenum is simple. Meckel's tract exhibits 

 two loops proximad of the diverticulum, while distad of it is a very wide area repre- 

 senting a supra-duodenal fold and an undifferentiated loop " c." The caeca are long and 

 the rectum is straight. In Sterna hirundo (fig. 56) the conformation is more apocentric, 

 and the pattern resembles that in many of the specialized Gruiform and Charadriiform 

 types. Meckel's tract is thrown into three minor loops, which, however, are better left 



SECOND SERIES. ZOOLOGY, VOL. VIII. 36 



