492 DR. P. CHALMERS MITCHELL ON THE 



Family Centetidje. Centetes ecaudatus (fig. 31, p. 491). 

 The duodenum cannot be distinguished from Meckel's tract as a separate loop. The 

 latter is relatively long, and is suspended in very regular minor loops at the periphery 

 of a nearly circular expanse of mesentery. There is no caecum. The hind-gut consists 

 of a short, straight, and rather wide rectal portion. The anterior mesenteric vein curves 

 round the Meckelian mesentery and is joined by a posterior mesenteric vein. 



Family Chrysochlorid^e. 



I have not examined any members of this family. Flower (5) states that the caecum 

 is absent. 



As the cgecum is absent in at least Tupaia tana, it is plain that the names 

 Menotyphla and Lypotyphla are not well chosen for the two divisions into which the 

 Insectivora are divided. I have already called attention to the extreme, almost 

 Keptilian, simplicity which characterises the gut-pattern of most of the Insectivora. 

 It cannot be assumed, however, that this simplicity is primitive. The absence of the 

 caecum is probably secondary, and the differentiation of the hind-gut in the Macro- 

 scelididae and in the Mole affords evidence of a formerly more complex condition in 

 the other forms. 



Order CHIROPTERA. 



Division Megachiroptera. 



Family Pteropodhxe. Pteropus gouldi, P. medius, Cynonycteris collaris. 

 In the Fruit-Bats the intestinal tract is relatively much longer than in the Micro- 

 chiroptera, a condition which is rather in contrast to that found in Birds ; fruit-eating 

 birds practically invariably have the intestinal tract much shorter and of relatively 

 wider calibre than occurs in their nearest insectivorous or seed- and grain-eating 

 relatives. In the Pteropodidee the duodenum is not a distinct loop. Meckel's tract has 

 a disposition almost exactly similar to that shown in fig. 31. The hind-gut consists 

 merely of a short, rather wide rectum, and there is no caecum. 



Division Microchiroptera. 



I have examined a number of Bats, chiefly Vespertilionidae. In all these the 

 intestinal tract is extremely short, consisting merely of a very short and slightly folded 

 loop, representing the duodenum and Meckel's tract, and suspended by a slightly 

 expanded mesentery, and a hind-gut consisting of a very short straight rectum. I 

 myself have seen no caecum, but Owen states that a short caecum is present in 

 Megaderma, one of the Rhinolophidae, and in Rhinopoma, one of the Emballonuridae. 



It is plain that the very simple gut of the Chiroptera cannot safely be asserted to be 

 primitive. 



