22 Dr Barclay-Smith, Extreme Visceral Dislocation. 



In most fishes the large gut is short and straight, a typical 

 rectum, which is marked off from the rest of the intestine by a 

 valve ; this valve with but few exceptions being circular in 

 arrangement. The first part this valve is called upon to play 

 is obviously to prevent regurgitation when the rectum becomes 

 involved by a contraction which results in the expelling of its 

 contents. 



In the herbivorous reptile, the valve recedes from the anal 

 orifice owing to the elongation of the large gut, and the presence 

 of a csecal diverticulum becomes established. The character of 

 the diet is obviously the influence which accounts for these modifi- 

 cations, and as undigested material in the form of grass, leaves, &c. 

 is often found in the colon, digestive changes, to a considerable 

 extent at any rate, must take place in this part of the gut. 



Of course it is possible that the mucous membrane lining 

 this part of the gut is capable of furnishing a secretion which 

 can deal with this vegetable material ; but judging from the 

 resistance displayed by vegetable material largely composed of 

 cellulose and chlorophyll to the influence of the digestive fluids 

 ordinarily furnished by the alimentary canal, this is hardly probable. 

 Further, from the constancy with which micro-organisms are found 

 in the large intestine as compared with the small, it is legitimate 

 to surmise that they are to be found in the large intestine in these 

 animals, and there play an important r61e in digestive processes. 

 If this be true, a herbivorous reptile is incapable of furnishing 

 digestive fluids which can satisfactorily deal with a considerable 

 part of its vegetable diet, and has to rely, partially at all events, 

 on the results brought about by parasitic micro-organisms. 



It, as will be afterwards pointed out, seems to be an economical 

 advantage that the activity of these micro-organisms should be 

 confined as far as possible to the large gut, therefore an elongation 

 of this part of the intestine in order to provide an increased 

 absorptive surface for the results of the microbic digestion, and 

 a caacal appendage at its proximal end whereby a more or less 

 stationary accumulation of the intestinal contents undergoing 

 digestive processes is assured, become physiological necessities. 



In order that the caecum may be filled and the stay of its 

 contents be prolonged, it is probable that the anti- peristaltic 

 wave becomes simultaneously established. This anti-peristaltic 

 wave is probably a simple modification of the rectal contraction 

 whose rdle is the simple one of discharge in the fish. The 

 presence of the circular valve is evidence that the contractile 

 wave makes itself felt in opposite directions in such an animal. 

 With the elongation of the rectum to provide a large intestine, 

 it is conceivable that the contractile wave, to a certain extent, 

 retains its primitive features, viz. starting in the middle of this 



