INTESTINAL TRACT OP MAMMALS. 



227 



have been almost unnecessary to draw a second figure but for 

 the fact that the colic loop is .in ansa coll dextra in Macro- 

 scelides, and probably is not so in Phalangista. 



In Talpa earopcea (text-fig. 23) the pattern is rather simpler. 

 The duodenal region is rather more distinct, although in the 

 diagram this is over-emphasised ; Meckel's tract consists of a 

 number of rather long minor loops occupying the whole of the 

 proximal limb of the pendant loop. There is no trace of a 

 caecum, and notliing else to indicate where the ileum passes into 

 the hind-gut. The recurrent loop runs straight up towards the 

 <lorsal middle line,and, just before bending round to form the 

 straight rectum, gives rise to a single very )iarrow and long 

 colic loop (an ansa coli dextra) which, in the unfolded condition, 

 is bent over towards Meckel's tract and shows a trace of spiral 

 twisting. 



Text-fiijure 22. 



Intestinal tract of MaorosceUdes species. 



S. Cut end of the gut nearest stomacli. K. Cut end of gut nearest rectum. 

 C. CtEcuin. C.L.I. Colic loop {ansa coli dextra). 



In Erinaceiis and in Gentetes (Mitchell, 1905, fig. 31), the 

 duodenum and Meckel's tract are not distinct. The latter is 

 arranged in very regular minor loops round the periphery of a 

 nearly circular expanse of mesentery. There is no trace of a 

 cfecum, or of a colic loop, but the recurrent limb runs up towards 

 the dorsal middle line, and then bends over to form a short 

 straight rectum. 



In the three types the whole gut is suspended on a continuous 

 mesentery, and the three appear to show stages in the attain- 

 ment of a secondary simplification, the stages of which are, first, 



15* 



