INTESTINAL TEACT OF MAMMALS. 453 



however, shows that only a relatively short part of the hind-gut is to be regarded as 

 rectum. The second point of difference is more important. The distal straight end of 

 Meckel's tract joins the conjoined caecum (C) and hind-gut at an acute angle, as in 

 Petaurus and Bettongia. But exactly opposite the uormal caecum there is a second 

 caecum (Ca), much shorter than the first, but quite distinct. Some years ago I 

 examined the caeca of all the Kangaroos that died at the Gardens, and was able to 

 satisfy myself that this relic of paired caeca is quite a common occurrence. I believe 

 it to be of considerable theoretical importance. 



The Diprotodont Marsupials are typically herbivorous forms, and, especially in the 

 larger Kangaroos, show an approximation in general character to the herbivorous 

 Eutheria. This resemblance or convergence displays itself in the intestinal tract, first 

 by a great increase in length in the portion known as Meckel's tract, an increase which, 

 although it is not sufficiently represented in the figures, is never so great as in the 

 Eutherian type. Next, it reveals itself in the complexity of the hind-gut. Here, also, 

 the essential difference between the convergent resemblances of a homoplastic nature 

 and resemblances showing affinity is manifest. In both Marsupial and Eutherian 

 herbivorous animals the hind-gut is lengthened, and the lengthening is associated with 

 the fundamental mammalian division of the hind-gut into colon and rectum. But in 

 no case is there the slightest approach to the special peculiarities assumed by the 

 long colon of Eutherian Herbivora. The gut-pattern remains that of the simplest 

 Mammalian type, and differs in no important morphological respect from that of the 

 carnivorous and insectivorous Polyprotodonts. 



The gut of Marsupials shows, under the differences associated with different habit, a 

 fundamental identity. It is simply a diagram of the primitive mammalian gut, 

 and this primitive character is further accentuated by the abundant traces in the 

 Diprotodonts of an originally paired state of the caeca. 



Sub-Class M O N O D E L P H I A. 



Order TUBULIDENTATA. 



Family Orycteropodid..*e. 

 I have not had the opportunity of examining Orycteropus. Flower (5), however, 

 dissected a specimen that died in the Gardens. He described the whole gut as being 

 extremely long, the duodenum and Meckel's tract together measuring thirty-two feet, 

 whilst the hind-gut was capacious and seven feet in length. There was a long single 

 caecum, with an expanded globular extremity. 



vol. xvn. — part v. No. 3. — December, 1905. 3 p 



