ON THE DIGESTIVE ORGANS, AND THEIR APPENDAGES. 143 



ferior to that in the feeders upon succulent vegetables ; and that among 

 the omnivorous rodents, as the Black Rat (Mus rattus, L.), the caecum 

 presents the smallest proportions, In many genera, especially of the 

 murine group, the large intestine, after its origin, becomes narrower, 

 and forms numerous spiral convolutions on itself, the number of turns 

 being sometimes six: this peculiarity is observable in the Hamster, the 

 Lemming, the Spalax, and others. 



In the marsupials a caecum generally exists ; in Phalangista the 

 caecum is long, and convoluted on the mesentery. In Dasyurus there is 

 no caecum. (See Account of Anat. of Dasyurus macrourus, in Proceed- 

 ings of Zool. Soc. 1835, p. 8.) In Didelphis the caecum is very short, 

 and simple. (See Account of Anat. of Didelphis Azarce, in Proceedings 

 of Zool. Soc. 1834, p. 102.) In the Kangaroo the caecum is rather larger, 

 and sacculated. In the Echidna the caecum is moderate ; but it is small 

 in the Ornithorhynchus. 



The entrance of the small intestine into the colon is generally valvu- 

 lar, even where the caecum does not exist ; except, indeed, in the Bears, 

 Weasels, Otters, &c., and also in the Dasyurus. 



The digested food having, in its passage through the small intes- 

 tines, parted with its chyle, the faecal part only is passed into the large 

 intestines, there to be accumulated, until nature requires its removal. 

 Where, however, the caecum, as in the Hare, is of extraordinary volume, 

 and the large intestines long and tortuous, it would appear that chyle 

 continues to be absorbed from the digested aliment in the colon, for a 

 considerable distance ; and, in carnivorous animals, destitute of a caecum, 

 this absorption most probably is continued till within a comparatively 

 short distance from the intestinal termination. The shortness of the 

 alimentary canal, the comparative simplicity of its course, and the absence 

 of a caecum, or, where present, its small size, together with the unsaccu- 

 lated condition of the colon, in carnivorous mammals, all tend to a quick 

 passage of the digested food, which, consisting of animal substances, 

 is assimilated with ease, while the excrementitious part, which might, 

 perhaps, run into a state of putrescence, has no impediments to delay 

 its expulsion.* In herbivorous animals, on the contrary, whose food 

 is of a lower kind of organization than that of the Carnivora, its delay 

 is requisite ; and, that none of the nutritious part be lost, it is passed 

 slowly over an extensive absorbing surface : hence the length and tor- 

 tuosity of the small intestines, the complexity of the caecum, puck- 

 ered into sacculi, and the sacculated or winding condition of the colon. 



* In an insectivorous animal, Echinops Telfairi, Mart., the intestinal canal, simple, and destitute of 

 a caecum, measures nine inches, being not even twice the length of the animal, which is rather more 

 than five inches. See Trans, Zool. Soc., 1839. 



