R. R. Bensley 145 
of such a stomach as that of Phocwena, Weber started from the a priori 
assumption that the first portion was of csophageal origin. The obser- 
vation of Jungklaus, 98, that the epithelium of the first chamber of 
the stomach of Phoceena becomes stratified at a very early stage of de- 
velopment is not, in my opinion, sufficient evidence in itself of cesopha- 
geal origin. 
In all other mammals, the evidence at present available is that the 
complex stomachs such as those of Ruminants, Rodents, etc., are pro- 
duced from a simple stomach by progressive specialization in which the 
cesophagus takes no part, and in which the important phenomena are 
the suppression of the gastric glands and the replacement of the mucige- 
nous epithelium by a stratified squamous epithelium. J urther investi- 
gatién may show the same to be true of the Cetacea. 
It now remains to examine, as far as present information permits, 
into the cause of the transformation and the stages through which it 
has passed. 
The changes which have taken place in the process of specialization 
in the stomach may be divided into two categories. To the first belong 
the changes of structure of the coats of the stomach more particularly 
of the mucous membrane; to the second, changes of form brought about 
by the expansion of certain portions of the stomach by the occurrence 
of constrictions dividing the stomach into successive chambers, or by 
the formation of saccular outgrowths. 
In connection with the first group of changes, namely those affecting 
the structure of the coats of the stomach, it has been already indicated 
that the salient features as far as the mucous membrane is concerned are 
the disappearance of the gastric glands and the replacement of the 
simple epithelium by stratified squamous epithelium. It remains to be 
seen by what steps this condition has been reached and what causes 
have been operative in producing them. 
An examination of the stomachs of Macropus, Sus and Tapirus in 
which the stratified epithelium has advanced but a short distance into 
the stomach, makes it extremely probable that the process of transfor- 
mation has begun at the wsophageal opening, has gradually spread over 
the fundus sac and the left portion of the stomach, finally encroaching 
in the same gradual manner on the right half of the stomach. A com- 
parison of the stomachs of Tapirus and Rhinoceros, Macropus and Dor- 
copsis is particularly convincing, the main difference being in the rela- 
tive extent of the non-glandular division which has expanded to in- 
clude the whole of the dilated fundus of the stomach in both Rhinoce- 
ros and Dorcopsis. In the Rodentia again, although, as far as we know, 
10 
