1902.] ADAPTATIONS IN DIPROTODONT MARSUPIALS. 17 



transversely very much elongated, but longitudinally quite 

 narrow, meshes. 



The figure (text-fig. 4) represents the blind end of the csecum 

 from the last sphincter, and shows also the transverse plicEe 

 described above. 



When the ceecum is filled the blind end seems to taper to a 

 point not unlike a vermiform appendix. 



The colon is thin- walled and smooth, only showing, in places 

 where it is contracted, longitudinal folds, which become efiaced 

 by stretching. 



From this description it will be evident that the c^cum of 

 Trichosuribs is an organ which has become to a considerable 

 degree specialized for digestion (and re-absorption). When the 

 chyme passes through the terminal portion of the ileum it 

 becomes mixed with the secretion of the glands of that intestinal 

 tract, to which is added, when it enters through the ileo-csecal 

 valve, the secretion from the caeco-colic glandular patch. Thanks 

 to the sphincters and the well-developed muscular coat of the 

 caecum, the food can be moved backwards and forwards, or retained 

 in the csecal divisions, and then be subjected to the action of the 

 glands through the development of an increased surface due to 

 the transverse plicse. This great specialization gives a satisfactory 

 explanation why the csecum of Trichosurus does not need to 

 grow out to such a size and attain such a capacity as that of the 

 Koala. It might be questioned whether any proofs can be given 

 to show that cellulose is really decomposed and digested in the 

 cfecum of this animal. It may then, firstly, be referred to the 

 peculiar structural specialization described above ; secondly, it 

 may be stated that the contents of the colon which have passed 

 the caecum seem to indicate such a digestion. There may still be 

 recognized remains of the most resistant parts of the vegetable 

 tissue, such as pieces of epiderm, isolated sclerenchym-cellules, 

 bundles of vessels, etc. — all of them looking as if they had been 

 cleaned by some reagent, so that only the hardest " skeletal " 

 parts were left. There are also to be seen the spiral threads, 

 these being the only remains of spiral vessels, the thin walls of 

 which probably have been digested. But I could not detect any 

 parenchymatous cellules or other softer parts. I think, there- 

 fore, that it may be admitted that the softer cellulose has been 

 decomposed and digested, leaving only the more or less lignin-like 

 substance. 



In Psetidochirus the small intestine is, as usual, thin-walled 

 and villous but otherwise smooth. The walls of the ileum do not 

 seem to show any increase in thickness. The ileo-cfecal valve (v.i.c.) 

 is well-developed, and from it extends as a transversal fold a 

 cseco-colic valve {v.c.c.) and sphincter, as may be seen in the figure 

 (text-fig. 5, p. 18). 



Close by, but on the colic side and also near the ileo-csecal 

 valve, a brownish glandular patch is seen, homologous with that 

 described above and in a similar situation in Trichosurus. (It is 



Proc, Zool. See— 1902, Vol. I, No. II. 2 



