1902.] ADAPTATIOXS IX DIPKOTODOXT MARSUPIALS. 21 



of t'ood-uiHteiial, and the mechanical pi'essure of this heavy load 

 might have produced expansions, which, if locaHzed, foTmecl bags 

 or sacculi. The first part of the colon might be expected to have 

 been strongly afiected by this pressure. It is consequently 

 natural that some wide sacculi should be formed there, and it is 

 these distensions which have been described and figured by the 

 authors as caecum, although they are derived purely from the 

 colon. It is also easy to undei'stand that when this distension 

 took plac^ the originally transverse cfeco- colic plica was drawn or 

 turned out of place to its present longitudinally-mnning direction. 



That the mechanical pressui-e of the contents of the colon 

 has really played important parts in transforming it to its 

 present shape, may also be proved by another fact. By a broad 

 band opposite the mesentery the colon is sacculated, which, of 

 course, is also an adaptation to its function. At the place where 

 the colon is most closely, by a very short mesentery, soldered to 

 the back of the abdominal cavity, the pressure of the contents 

 would, thanks to this fixation, be more efiective. There has thus 

 been formed two large sacculi, wliich give the colon at that place 

 ii size amounting to twice that of its usual mdth. The shape and 

 size of these sacculi are identical in two specimens which I have 

 seen. This confirms the correctness of the statement ; and I think 

 it is these which Owen means when he says : " One of these 

 sacculi was so mvich longer than the rest as to almost meiit 

 special notice as a second caecum." 



Peyer's patches of comparatively large size, 1 to 2 cm. in 

 diameter, are scattered in considerable numbers in the walls of 

 the colon, especially in its middle parts. 



The material which 1 have used for this study has long been pre- 

 served in spirit, and the measurements are perhaps therefore not 

 so much to be relied upon. It may, however, be mentioned that the 

 small intestine measured in one specimen about 410 cm., the ctecal 

 rudiment 6 cm. fi-om its blind end to its opening, and the large 

 intestine 840 cm. The "secondary caecum " is situated nearly at 

 the middle, or 430 cm. from the end. Even if these measure- 

 ments are imperfect in the detailed statements, they show satis- 

 factorily that the large intestine has been strongly developed. 

 Probably it is fully eight times the length of the animal, or even 

 more than in the Koala. 



The interior surface of the duodenum in Phcdanger shows 

 very plainly a reticulate sti'uctui'e, larger primary and smaller 

 secondary plicae may easily be distinguished. It offers thus some 

 faint resemblance in apjjearance to the structure of the reticulum 

 of a ruminant. The plicte ai-e in both cases formed by coalescence 

 of papillae. The villi of tlie intestine are well developed on the 

 ridges forming the network, but some are also scattered in the 

 interspaces. Lower down the small intestine this reticulate 

 structvxre is less conspicuous, but my material is not in such good 

 condition that I can say where it entirely disappears. The 

 jejunum appears, however, quite smooth, 



