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ANIMAL INTELLIGENCE. 
It is truly an astonishing fact that animals should 
engage in such vast architectural labours with what 
appears to be the deliberate purpose of securing, by 
such very artificial means, the special benefits that arise 
from their high engineering skill. So astonishing, indeed, 
does this fact appear, that as sober-minded interpreters of 
fact we would fain look for some explanation which would 
not necessitate the inference that these actions are due to 
any intelligent appreciation, either of the benefits that 
arise from the labour, or of the hydrostatic principles 
to which this labour so clearly refers. Yet the more 
closely we look into the subject, the more impossible 
do we find it to account for the facts by any such easy 
method. Thus it seems perfectly certain that the bea- 
vers, properly and strictly speaking, understand the use 
of their dams in maintaining a certain level of water. 
For it is unquestionable that in the solid-bank dams, as 
already observed, a regular opening or trough is cut at one 
part of its crest to provide for the overflow ; and now it 
has to be added that this opening is purposely widened or 
narrowed with reference to the amount of water in the 
stream at different times, so as to ensure the maintenance 
of a constant level in the pond. Similarly, though by 
different means, the same end is secured in the case of the 
stick dams. For 6 in most of these dams the rapidity or 
slowness with which the surplus water is discharged is 
undoubtedly regulated by the beavers ; otherwise the level 
of the pond would continually vary. There must be a con- 
stant tendency to enlarge the orifices through which the 
water passes,’ when the stream is small, and vice versa ; 
otherwise the lodges would be either inundated or have 
their sub-aquatic entrances exposed . 1 Moreover, a very 
little consideration is enough to show that in stick dams 
the tendency to increased leakage from the effects of per- 
colation, and to a settling down of the dam as its materials 
decay from underneath, must demand unceasing vigi- 
1 In times of considerable ‘freshet’ the former case sometimes 
occurs ; the beavers not being- able to provide for a very considerable 
overflow through their dams, the latter become then wholly submerged. 
When again expos od, the animals take great pains in repairing the in- 
juries sustained. 
