INTESTINAL TRACT OF MAMMALS. 213 



Whalebone Whales, that were there no other reason for associating 

 these creatures, it would be impossible to place them far apart, and 

 it must be inferred that, so far as the gut-patterns afford indica- 

 tions, tlie Toothed Whales are more highly modified than the 

 Whalebone Whales. If we are to seek for indications of the affini- 

 ties of the Cetacea, it must be from the Mystacoceti, and not from 

 the Odontoceti, tliat we start. The ditficulty is that a veiy simple 

 and primitive gut-pnttern affords few indications. It is plain 

 that the Cetacean gut-pattern shows no trace of special resem- 

 blances with the patterns of the Ungulates or of the Sirenia. 

 There is some indication of similarity with the gut-patterns 

 of the aquatic Carnivores (see Mitchell, 1905, fig. 32, and 

 text-figs. 26 & 27, infra), but the more distal position of the 

 csecum {i. e., tile greater distance from the apex of the pendant 

 loop) and the lengthening of the hind-gut in the Carnivores 

 present notable difterence. Unfortunately, we do not know the 

 gut-patterns of extinct mammals, but, so far as may be judged 

 from Carnivores and Insectivores, it seems probable that the 

 Creodonts had an alimentary tract showing a simple pattern 

 much like those suggested in text-figs 1 A and 1 B of this 

 memoir. The most notable peculiarity in the Cetacean pattern 

 is the position of the coecum towards the a.pex of the pendant 

 loop, a peculiarity that occurs also in the Monotremes and some 

 of the Edentates. The lengthening of the gut a.nd mesentery in 

 the longitudinal axis of the body, the great increase in the 

 number of the minor loops on Meckel's tract, and the retention 

 of the importance of the primitive mesentery ai'e such adaptive 

 characters as might be expected in animals that had taken to an 

 aquatic life. The gut-pattern of the Cetacea, then, is compatible 

 with the view that Cetacea represent a, very primitiA'e stock, 

 long adapted to aquatic life. 



Order Artiodactyla. 



Sub-Order Non-Ruminantia. 



Family Hippopotamidfe. Jlipjwpotamus amphibias (text- 

 fig. 16). 



The duodenum and Meckel's tract are not sharply marked off 

 from one another. This part of the gut is extremely long (in 

 text-fig. 16 it has been somewhat simplified), and is thrown into 

 numerous minor folds compactly crowded on the periphery of an 

 oval expanse of mesentery. There is no cpecum, but an increase 

 of calibre towards the apex of the pendant loop seems to mark 

 the point where, on the recurrent limb of that loop, the fore-gut 

 passes into the hind-gut. The distal portion of the recurrent 

 loop is thrown into a set of very large minor loops, attached to 

 the edge of the mesenterial expanse opposite to that suspending 

 Meckel's tract, and therefore representing a.n atisa coli dextra. 

 The distal end of tliis colic loop, or series of minor colic loops, 



