OCR Text |
Show 1902.] ADAPTATIONS IN DIPROTODONT MARSUPIALS. 19 The digestion in the caecum seems to be rather complete, since at a distance of 25 cm., more or less, from the ileo-caecal valve the faecal matter is already formed into balls. A microscopical investigation of these faecal remains shows that they are chiefly composed of pieces of thick-walled epiderm, bundles of vessels, isolated prosenchyme-cells, and similar matter. But the softer vegetable tissue has disappeared and the spiral threads of the vessels are isolated, indicating a digestion of the substance that once formed the walls. The intestine of the Koala has been described, as already mentioned, by the authors quoted above. Only a few remarks will therefore be made here concerning the intestine of a marsupial foetus of this species measuring about 9 cm. in length. Its small intestine measured about 37 cm., the caecum 8*5 cm., and the large intestine about 29 cm. The length of the three different parts of the intestine, compared with the length of the foetus itself, is thus expressed by the' following percentages: 411, 94, 322. If these now are compared with the corresponding ones from a grown animal, calculated from Forbes's measurements (see above), the difference is quite striking with regard to the caecum and the large intestine. The former is proportionately only about a third as long in the foetus as in the full-grown animal, and the latter less than half as large in the foetus as in the adult. The difference of the small intestine of both stages is not so great, that of the foetus being about four-fifths of the same in the adult. It is also to be remarked that in tha foetus the small intestine is considerably longer than the colon, but in the adult the reverse condition prevails. These differences can of course be ascribed to the difference of the diet of both stages. The milk food of the foetus is chiefly or completely digested in the small intestine, but the vegetable diet of the adult needs a greatly developed caecum and colon. The longitudinal folds of the caecum and the colon are, however, already developed in the foetus. The condition found in the Wombat is very peculiar. The narrow opening of the ileum protrudes, surrounded by an " ileo-caecal " valve, into the colic cavity. This valve has very broad lips, and within the same opens the lumen of the " processus vermiformis" (Owen), only separated from the opening of the ileum by a septum-that is, in other words, the terminal portions of the vermiform appendage and of the ileum are thus fused together into one structure protruding into the colon ; both open with separate orifices, which are, however, surrounded by the lips of the same valve. The glandular patch described above as situated near the valvida cceco-colica in the related Phalangerids is found in this animal too, but extends partly on to the outer side of the " ileo-caecal " valve itself already mentioned. From this latter valve plicae extend on two sides. These plicae seem to stand in the same kind of connection to the ileo-caecal valve as in normal cases the caeco-colic valve does. But they do not extend 2* |