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lakes as those of Switzerland and Italy. From his own investi- 
gations in the Alps and Britain he was of opinion that a glacier 
could only erode a rock-basin under certain exceptional cir- 
cumstances. . After describing these, he stated that he was 
inclined to refer the rock-basins about Snowdon to the later 
period of glaciation. He also thought that such causes as 
change in the eccentricity of the earth’s orbit, the effects of 
precession, and the alteration of sea and land, were more likely 
to have caused the glacial period than any variation in the 
sun’s heat. 
Mr Exits enquired how Mr Kingsley obtained the true 
depth when wind was blowing, and therefore the line not 
vertical, owing to the drifting of the boat. 
April 19, 1875. 
The PRESIDENT (PROFESSOR BABINGTON) in the Chair, 
(1) On the Mode of Formation of the Alimentary Canal 
in Vertebrata. By ¥. M. Batrovr. 
The author stated that the simplest type of vertebrate de- 
velopment was that exhibited by Amphioxus, and that all the 
complicated types found amongst other vertebrates were to be 
looked on as derivatives from this single type. 
He shewed that in Amphioxus the alimentary canal was 
formed by a simple invagination; that in the Frog the invagi- 
nation had ceased to be symmetrical and single as in Amphi- 
oxus, but had become unsymmetrical and had acquired other 
peculiar characters. 
In the Selachian’s development, which was to be looked 
upon as the type most allied to that of the Frog, the imvagina- 
tion was no longer present, but traces of it still remained. The 
