460 DE. P. CHALMEES MITCHELL ON THE 



The order Xenarthra, containing the Sloths and Anteaters, shows a definite and 

 characteristic pattern of the intestinal tract. The typical mammalian characters, the 

 rather incomplete separation of the duodenum, the simplicity of Meckel's tract, and 

 the division of the hind-gut into colon and rectum, are all present, without any special 

 elaborations. The typical veins are similar to those in the Marsupials, an anterior 

 mesenteric curving round Meckel's tract, and a posterior mesenteric or rectal vein. 

 The inference seems to be obvious that in this respect the Xenarthra have retained a 

 primitive arrangement, possibly the arrangement that existed in the "Reptilian stock 

 which gave rise to Mammals. The special feature of the gut of the Xenarthra is the 

 actual presence of paired cseca in the Dasypodidae and the presence of traces of an 

 original paired condition in the Myrmecophagidae and Bradypodidae. As similar 

 traces of a paired condition occur amongst the Marsupials, I think it a probable 

 inference that in the primitive Mammal the caeca were paired. 



The orders Tubulidentata, Pholidota, and Xenarthra are usually grouped together 

 as Edentata, although there are no very definite characters uniting them. The 

 evidence afforded by the patterns of the intestinal tracts gives no further reason for 

 regarding the group as coherent. I have not myself examined Orycteroptis, but as 

 that animal is stated to possess a long gut and good caecum, it obviously differs in this 

 respect from other Edentates. Any resemblances between Manis and the Xenarthra 

 are just as clear between the Xenarthra and many Marsupials ; they depend merely on 

 the fact that in all these animals the pattern of the gut is primitive, and the common 

 possession of a primitive condition of a set of organs, although it may be of convenience 

 for artificial classification, gives no evidence that can be applied to the- construction of 

 a classification based on affinity. 



Order HYRACOIDEA. 



Family Hyracid^e. Hyra.r capensis (fig. 14). 

 The intestinal tract of this animal is very peculiar. The duodenal loop is definite, 

 more definite than in the figure, being longer and rather narrower. The next area of 

 the gut is easy to interpret, if for the moment consideration be omitted of the peculiar 

 expansion marked A.C. in the figure. Neglecting that, Meckel's tract may be 

 described as fairly normal, thrown into regular minor coils that lie at the circumference 

 of an approximately circular outgrowth of mesentery, corresponding to the pendent 

 loop of mammalian embryology. At its distal extremity this passes into the hind-gut, 

 the latter occupying, as in many Mammals, a portion of the mesentery of the pendent 

 loop. The transition from Meckel's tract to the hind-gut is marked by a pair of caeca, 

 which again, if we still omit consideration of the caecal expansion on Meckel's tract, 

 we should interpret at once as a well-developed pair of caeca, homologous in position 

 and relations with the less developed pair of caeca of the Xenarthra. The hind-gut is 



