So pee 
572 The American Naturalist. [June, 
ee 
rather than the slight or rapidly recurring vibrations of its lateral 
walls. (II) The ossicles under consideration are accessory to the 
hydrostatic function of the air-bladder. (IIIT) The Weberian mechan- 
ism is of great functional importance to the fish possessing it, since it 
confers on them an exceptional capacity for freedom of locomotion in 
a vertical direction. The possession of this mechanism permits all 
movements to be made with the maximum economy of muscular effort 
and tissue metabolism. 
In regard to the evolution of the Weberian mechanism the authors 
reach the following tentative conclusions: i 
1. The special feature of a fresh-water habitat that has conditioned 
the development of the Weberian mechanism in the Ostariophysex is 
the occurrence of seasonal or periodic quantitative variations in the 
food supply, variations to which the Ostariophysex, from their herbiv- 
orous or omnivorous habits are specially liable. ; 
2. In view of such unfavorable nutritive conditions, the special 
advantage which is conferred upon the Ostariophysex by the posses- 
sion of the Weberian mechanism is a capacity for executing locomotor 
movements in any plane, with an almost irreducible minimum 0 
muscular effort and tissue metabolism. 
3. If a variable and inconstant food supply is to be regarded as one 
of the inevitable conditions of a fresh-water existence, and necessitates 
strict economy in the expenditure of muscular energy, any mechanism 
which secures this result must be of unquestionable importance to the 
species, and hence it may be that the Ostariophysee owe their domi- 
nant position among fresh-water fishes to the possession of the Weber- 
ian mechanism. 
4, The evolution of the Weberian mechanism has not only condi- 
tioned the predominancy of the Ostariophyses, but, indirectly, has 
favored the existence in fresh water of a large number of purely car 
nivorous fishes, which depend on the former for their food, and there- 
fore may also be regarded as one of the primary causes of the anomal- 
ous abundance and diversity of fresh-water piscine life, as compared 
with the remarkable poverty of all other groups of fresh-water organ- 
isms. (Proceeds. Roy. Soc. Vol. LII, 1892). 
Age Modifications of the Mucous Lining of the Stomach 
of Ruminants.—In a study of the Comparative Anatomy of the 
Stomachs of Ruminants, Mr. J. A. Cordier has discovered the follow- 
ing interesting facts. es 
The interior of the stomach of a young adult is covered with papille 
closely packed, which are larger in the region which Wilkins calls the 
