140 ME. P. CHALUEKS MITCHELL ON THE [Jan. 14, 



end — extension of gut — has been attained in different groups, would 

 seem to offer a field of enquiry that may ultimately give important 

 results bearing on the problem of divergent evolution. Dr. Gadow 

 has shown that the modes of coiling the gut have systematic 

 value : so far as my material has been able to take me, it looks as 

 if the divergencies were grouped indifferently around the common 

 type. 



R A T I T ;E. 



In the Cassowary (fig. 3) the common type is retained with an 

 almost diagrammatic simplicity. The duodenum is a short, very 



Fig. 3. 



Casuaritts ; intestinal tract. 



wide loop, and presents the peculiarity, which may have been 

 an individual abnormality in my specimen, that the hepatic and 

 pancreatic ducts open on a wide diverticulum of the distal limb of 

 the loop. The circular fold of mesentery has the very slightly 

 folded gut suspended at its circumference, and the remains of the 

 yolk-sac appear as a short esecutn in the middle of the loop. The 

 rectum is short and straight, and the caeca are in the typical 

 position. The blood-vessels are absolutely typical. ■ 



The Emu which I examined (Dromcetts novce-hollandice) was 

 identical in its main features with the Cassowary, and it is 

 unnecessary to give a separate drawing. The duodenum was 

 narrower aud longer, and the hepatic and pancreatic ducts opened 

 separately into the duodenum, not upon a common diverticulum. 



The Ostrich(fig. 4), which was the fine male known as the Queen's 

 Ostrich, presented an important deviation. The first two parts of 

 the intestine and the three great veins were according to type, 

 the yolk-sac diverticulum being conspicuous on the circular loop 

 opposite the end of the median mesenteric vein. The distal limb 

 of the duodenum presented a short lateral diverticulum, and the 

 cseca are relatively longer than in Casuarius and, aa has been 



