352 Stapley and Lewis : 



August last, the caecal changes due to food were dealt with. It 

 remains for us to point out that although the state of the bowel 

 development depends wholly upon food taken undgr the process 

 of natural selection, yet when deductions are drawn from, com- 

 parative anatomy, those deductions must be controlled by a 

 knowledge of the trend of the order. A study of mar- 

 supials, for instance, creates the belief that marsupials 

 are more responsive to food change than primates. The 

 extreme atrophy of the caecum in the wombat occurs on a 

 nutritious diet composed wholly of vegetable matter. When 

 we reflect on the fact that the koala nourishes its tissues wholly 

 on gum leaves, we are struck by the wonderful constructive power 

 of the koala's (Fig. 19) intestines, which convert into strong 

 animal tissues that Avhioh to other animals is an indigestible 

 poisonous scented fibre. This higher digestive efficency explains 

 why the wombat sliows caecal atrophy upon a diet which, 

 if taken by man, would require a considerably larger caecum 

 than he has now. 



The difference between type D, human appendix, and the 

 wombat's appendix is one of distortion. The human appendix 

 being distorted by erratic peritoneal adhesions, the wombat's 

 appendix being straight. 



An amendment of Treve's four types of caecum is necessary, 

 because in those types is not included the foetal type, which 

 differs from type A in showing no longitudinal muscle bands. 

 Preappendicular types — 



T}'/>e A, No. 1 — Foetal caecum. No bands. (Fig. 12). 

 Type A, No. 2 — Infantile caecum. Banded. (Fig. 8 A). 

 Appendicular types — 



Type B — The earliest appendix or f undal appendix. (Fig. 8 B). 

 Type C — The intermediate appendix. (Fig. 8 C). 

 Type D — The late or ileo-caecal appendix. (Fig. 8 D). 

 The foetal caecum is proportionately bigger than the adult 

 caecum (man). 



Foetal measurements (8 months estimated) — 



Stomach and small intestines - 1.04 metres 

 Caecum - - - - - , .06 „ 



Large intestines - - - .24 „ 



