1902.] ADAPTATIONS IN DIPROTODONT MAKSUPIALS. 25 



somewhat shorter in the young than in the adult. The difference 

 is, however, not so great as in the case of a marsupial foetus of 

 the Koala already mentioned. Although the latter represented 

 a younger stage \ the conclusion can thus be drawn that the 

 milk diet of the young Petaurus differs, with regard to its com- 

 position and therefrom resulting influence on the intestine, less 

 than it does in the case of the young Koala. It is also of 

 interest to note that in the young Petaurus the cfecvim stands in 

 quite open communication with the colon. That is because the 

 sphincter is not needed yet for the purpose of prohibiting any 

 indigestible remains from entering the csecvim as in the adult. 



In Acrohates the arrangement of the connection between 

 the small and the large intestine is the same as in the adult 

 Petaurus. The ileum opens with its valve protruding like a 

 mouthpiece into the colon ; and there is a very strong constric- 

 tion between the latter and the csecum. Although the stomach 

 in my specimen of Acrohates was empty, I think it may be 

 assumed that it lives on a similar diet to Petaurus ; and at any 

 rate the function of the csecum seems to be perfectly alike in 

 both animals. 



The small intestine of Acrohates is comparatively shorter even 

 than that of Petaurus. In the latter and in Phalanger the 

 length of the small intestine is comparatively not much different. 

 This may be understood as meaning that that part of the food- 

 material which ought to be digested in the small intestine of 

 Phalanger is not difficult to digest. It may chiefly consist of the 

 juice and other contents of the soft parenchymatous cells of the 

 fruit-pulp. This matter is, of coiu^se, more easily accessible for 

 the digestive organ than is the material contained in the better 

 protected cells of the leaves etc., which form the food of the 

 animals considered above, and the small intestine of which, there- 

 fore, has become lengthened. 



As the last stage in this series, showing a different develop- 

 ment of the intestine and especially of the caecum in accordance 

 with the different diet, Tarsipes may be mentioned ; this animal 

 has, as already remarked, entirely lost its csecum, because such an 

 organ is superfluous for a honey-eater. 



The general arrangement and structure of the dentition of 

 these animals indicate that also with regard to those parts adapt- 

 ations for different purposes have taken place. The dentition of 

 Phascolotnys is evidently most specialized. Its incisors are more 

 reduced in number than in the others, the canines are absent, 

 and the molars have persistent pulps. The latter are also curved 

 in such a way that the upper molars are laterally concave and 

 the lower ones are laterally convex. This development and shape 



1 The Koala foetus was still naked. The young Petaurus was beginning to 

 become hairy, so that, for instance, the dark vertebral stripe was well conspicuous, 

 but the hairs of the tail were not j^et prolonged. It had certainly not j-et partaken 

 of any other food than inilk, because the mandibular incisors, although pi-otruding 

 3 mm. from the sockets, had not cut the gum. 



