150 The Cardiae Glands of Mammals 
the new outlet of such a nature that the parietal and chief cells had dis- 
appeared from the glands and their places had been taken by muciparous 
elements similar to but not identical with those normally found in the 
neck of the gland. It might of course be urged that these changes had 
been of inflammatory origin due to the surgical injury inflicted but it 
seems more reasonable to suppose that they have been due to the fact 
that a new focus for the motor activities of the stomach has been set 
up and that this coincides with the opening into the intestine. If such 
change can be produced in the life of a single individual by surgical 
interference, it is not difficult to believe that just such simple causes 
acting through many generations and assisted by the processes of natural 
selection have produced the changes which we see in so many herbivors 
belonging to both the placental and marsupial series. 
As to the precise way in which the factors enumerated above have 
acted, very little can be said because there is as yet no experimental 
evidence on which to base conclusions. Possibly limitation of the blood 
supply to the mucous membrane owing to the pressure exerted by the 
great bulk of food, and exhaustion of the glands from continued over- 
secretion may be of importance, while actual friction will explain the 
change in the surface epithelium. 
A further argument in favor of the view that the changes in the 
stomachs of herbivorous mammals owe their origin to mechanical causes 
aided by natural selection, is afforded by the occurrence in the sloth, in 
the camel and the llama and in the peccary of saccular diverticula lined 
by cardiac glands. If the hypothesis that the cardiac glands are the 
intermediate stage in the disappearance of the glands, be correct, it is 
easy to understand why they have been retained in these animals. Sup- 
pose, for example, that an animal is undergoing a change of habit of 
such a nature that it is passing from an omnivorous to an herbivorous 
diet. The effect of this would be, if the above hypothesis is correct, to 
cause the transformation of the fundus glands in the neighborhood of 
the cardiac orifice into cardiac glands and finally the disappearance of 
the latter and the conversion of the epithelium into stratified epithe- 
lum. If, however, in the portions of the stomach where these changes 
were taking place, sacculation occurred, the mucous membrane of such 
a saccule would be less exposed to the disadvantageous action of the 
prolonged presence in the stomach of a food mass of firm consistence 
or of the friction caused by the movement of the latter over the sur- 
face of the mucous membrane. It would be less likely to come into 
contact with the freshly-swallowed food or to be subjected to sudden 
changes of temperature. The result would be that the degenerative 
