Finally, Each And Every Line Manifests Extraordinary Variability In The '30's. It Is Not To Be Supposed That The Population Fluctuated So Enormously From One Year To Another, But Rather That The Facilities For Export Were Irregular.

The case is further complicated by the fact that some of the totals represent part of this year and part of last; nevertheless, upon the whole, the following general principles are deducible:

(A) The high points for each species are with fair regularity 10 years apart.

(b) In the different species these are not exactly coincident.

(c) To explain the variations we must seek not the reason for the increase - that is normal - but for the destructive agency that ended the increase.

This is different in three different groups.

First. The group whose food and enemies fluctuate but little. The only examples of this on our list are the Muskrat and Beaver, more especially the Muskrat. Its destruction seems to be due to a sudden great rise of the water after the ice has formed, so that the Rats are drowned; or to a dry season followed by severe frost, freezing most ponds to the bottom, so that the Rats are imprisoned and starve to death, or are forced out to cross the country in winter, and so are brought within the power of innumerable enemies.

How tremendously this operates may be judged by these facts. In 1900 along the Mackenzie I was assured one could shoot 20 Muskrats in an hour after sundown.

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