NATURAL HISTORY XOTKS 
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the inherited experience of countless generations as to what is best for the 
species or race in each case. It is still instinct, but inherited and constantly 
being changed and perfected to meet ever-changing conditions of life, not 
endowed as a fixed and unchanging characteristic, and it is still blind, i.e., in- 
voluntary and unreasoning. Man has inherited numerous instincts, all of which 
were useful to him in his primitive days and most of which would be useful 
now ; but he has almost extinguished many of them by the exercise of what he 
calls reason — save the mark 1 — and consequently he is tbe poorest animal on the 
face of the earth and the only animal that cannot keep itself in good health. 
Some of his instincts still survive, such as the involuntary shutting of the eyes 
when threatened suddenly. 
Now, with all animals and plants the predominating necessities are food and 
reproduction and everything else is subservient to these — the continuance of 
life and the continuance of the species. If Mr. Daubeny grants this, will he sa^ 
which of these two he prefers as the motive power of migration, or will he do 
what he has not done so far, and that is, suggest something better? Personally, 
I believe that “ food is the determining power in migration, and that reproduc- 
tion takes place where there is the most suitable supply for each spec es during 
the increased demand.” Migration is a far more general thing than most people 
think ; in fact it would be almost safe to say that all birds migrate — not neces- 
sarily to other countries, but to other counties, fields, woods or pastures new, 
as the case may be ; and there seems little doubt that food is the determining 
factor in these migrations, at any rate. I would explain the custom of some 
.species to migrate early by the persistence of a habit acquired by those species 
in the remote past, when, perhaps, geologic conditions were not quite the same 
as now and the arctic regions extended turther south. The birds remained in 
tenqierate or northern regions until, with the approach of winter, cold northerly 
winds began to blow, and then they flew with those winds towards the south, 
those which neglected to fly perishing. The descendants of the survivors would 
inherit the tendency to fly, and this would gradually become fixed at a certain 
time, which would remain unchanged through generations until some great cause 
intervened to bring about an alteration. Hence, it was good for these species 
to migrate north or south at a certain time, and so they do it now by virtue of the 
inherited experience of their ancestors right back to remote times. They find 
their way by the simple means of recognition by sight of well-known landmarks 
passed by them before, and young birds are able to do so because there are some 
old birds with the flock to lead them. Should a contrary wind blow them out 
of their course, they sometimes lose their hearings and perish in the sea or 
otherwise. 
I wish it to be distinctly understood that I here summarize the ideas I have 
picked up on the subject and do not advance them as my own, because I have 
had few opportunities of studying the migration of birds, not having lived in the 
country. What I have here set down I consider satisfactory. Mr. Daubeny 
drags insects into the discussion, but I must point out that the travels of 
insects are not migrations, but emigrations — a very different thing. Migration 
implies return ; emigration does not. Almost all orders of insects appear to have 
supplied instances of emigration and in many cases food seems here also the 
determining factor, as for instance, with locusts and cockroaches. The motive 
does not seem to have been determined in the case of butterflies and moths, 
which furnish, perhaps, some of the most obvious examples of emigration. It 
appears, however, that there is a general tendency for insects whose natural 
habitats are north of the equator to go north and for those in the south to go 
south, so that there is a deeply-rooted instinct towards emigration ; and 
as it appears to be generally conceded airiongst entomologists that Orthoptera 
(including locusts and cockroaches) are amongst the most ancient, if not the 
most ancient, of the orders of insects, the dispersive tendency originating in 
them has been transmitted to their derivatives with, of course, a progressively 
weakening effect, the farther removed in point of evolution the more recently 
developed orders (such as Lepidoptera, Diptera, and Coleoptera) are from the 
primitive type. 
Hale End, Chingford. 
C. Nicholson. 
