300 The Field Naturalist's Quarterly November 



snake had swallowed head first a large frog of some species. 

 As before, the anterior half of the amphibian was disin- 

 tegrated by digestion, the head, both fore-limbs, and one 

 hind-limb which had been pushed forwards in the act 

 of swallowing, being quite untouched. As before, the food 

 was fixed at the constricting entrance. 



These two specimens settled the point ; and it then 

 occurred to me that if one had thought at first of estimating 

 the capacity of the stomach, and comparing it with the 

 bulk of some of the animals which form the food of snakes, 

 one could have foretold the result theoretically. I have 

 mentioned that this mid-gut is very small, in the adder 

 only a little more than 3 inches long. But the adder 

 feeds on slow-worms, it may be, 1 2 inches in length, 

 mice, voles, birds, etc., none of which could be contained 

 whole in the stomach. It is therefore obvious that some 

 arrangement is necessary to allow of the food being passed 

 into the mid-gut gradually, and being digested as it does so. 

 That this actually is what happens these examples show. 



This process, in all probability, explains in part why 

 serpents feed at such long intervals. I am not able to 

 state how long it takes for an adder to digest a slow-worm 

 a foot long, but it must be some considerable time ; and 

 while the process is in course of completion, it is not likely 

 that the snake will take in further food. 



One other point is suggested. It seems evident that 

 the serpent can retain food in the gullet for some time 

 undigested. That is shown by the first case quoted, in 

 which the vole swallowed last was untouched. It would be 

 interesting to find out whether the snake can pass on the 

 food at will, or whether the process is involuntary. It can 

 certainly eject swallowed food at will, so that possibly it 

 can also control the rate at which it digests. 



Since these specimens were of widely different species, 

 it is a fair assumption that this mechanism of digestion is 

 common to the Order Ophidia, and as far as I know is 

 found in them alone. 



The two specimens and their food, in course of 

 digestion, are now in the Zoological Museum at Edinburgh 

 University, 



