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THE PKINCIPLES OF BIOLOGY. 
(d.) As nerve force. This is also seen to be dependent 
on the same breaking down of complex substances. 
(e.) As sensible motion. The most evident of the “ re¬ 
actions called forth from organisms by surrounding 
actions.” This manifestation of force is not con¬ 
fined to the Animal Kingdom, being commonly 
exhibited by certain of the humbler plants, as well 
as in the circulation of the sap in higher forms. 
Mechanical motion is nevertheless specially 
characteristic of animal life, and in its highest 
manifestations is always effected by the contraction 
of muscle under the impulse of nervous stimuli. 
Mr. Spencer suggests that the important changes 
involved in the contraction and relaxation of 
muscle may be explained by the repeated occur¬ 
rence of an isomeric change in its molecular 
constitution. 
ANNUAL MEETING OF THE UNION. 
The Midland Union of Natural History Societies will this year 
travel to the eastern verge of its district, in accordance with the 
invitation of the Peterborough Natural History Society. The 
annual meeting will be held at Peterborough probably in the latter 
part of June, and very attractive excursions are being arranged by 
the local committee. Situated on the border of the Fens, yet 
surrounded by excellent and remarkable sections in the oolitic strata, 
Peterborough offers attractions of a high order to the botanist, the 
entomologist, and the geologist, while the archaeologist can revel in 
the buildings and churches of the town and neighbourhood. We 
trust that the members of the Union will muster in large numbers to 
avail themselves of such an excellent opportunity of exploring “ fresh 
scenes and pastures new ” under able and judicious guidance. 
Yeab-Book of Scientific Societies. —Messrs. Griffin & Co., of 
Exeter Street, Strand, have in hand a work which will give much 
information respecting the scientific and learned societies of Great 
Britain. It will be edited by Mr. W. B. Browne and Mr. Barclay. 
Secretaries of societies in the Midland Union should at once put 
themselves in communication with Messrs. Griffin, who will forward 
them a form containing the points on which information is desired for 
publication. 
