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THE entomologist’s RECORD. 
colour) will have an advantage if the species rests on trees, 
rocks, etc.. No. 4 a greater advantage than No. 3, and so on ; 
and vice versa in a dry season {vide Diag. i). 
“ Now let us suppose the same species to vary, independently 
in its relation to dryness and damp, con- 
stitutionally. Let us arrange it again dia- 
grammatically {vide Diag. 2), in order thus : — 
“ Then the individuals of No. i thrive best 
when dry weather pushes them on rapidly, 
but die in wet. No. 5 gets on well and 
strongly in damp weather, but dies in dry. 
(These I mean as tendencies, of course). Now 
if we superpose these diagrams {vide Diag. 3), we have a set i-i, 
that is doubly favoured by hot weather, viz., is pale in colour 
and suits the weather constitutionally ; another set, 5-5, is 
doubly suitable to damp weather, viz., is dark in colour and 
suits the weather constitutionally ; the occupants of the other 
squares are in intermediate positions. In a variable climate, 
like that of the British Isles, it is obvious that, in some 
seasons, i-i would be highly favoured, in others, 5-5 ; 
whilst the others, 1-5, 2-3, 3-2, 5-1, etc., would always be 
at a relative disadvantage, and we should in course of time 
have a race consisting of i-i and 5-5, freely crossed together. 
In a series of dry seasons, i-i would predominate, after a 
series of wet seasons, 5-5.^ Now what would the effect of 
I-I and 5-5 crossing together be ? Chiefly, probably, they 
would result in a race indistinguishable from 3-3, but they 
would possess the potentiality of readily, under suitable con- 
ditions, evolving i-i or 5-5, which 3-3, if bred true in an 
uniform climate would not possess. Each individual is, 
though to appearance 3-3, really nothing of the sort, but a 
combination of i-i and 5-5, capable by selection of being 
easily sifted apart, and the pure race of, say, i-i, evolved in a 
few generations, whereas it would require a long period to do 
so from a pure race of 3-3. Now the question I ask is this : — 
Will it result also that the i-i element and the 5-5 element in 
each individual exist in a so far independent state that if 
placed in circumstances favourable to i-i, it will predominate 
in that individual, or, if in circumstances favourable to 5-5, 
the 5-5 element will assert itself during the life of that indi- 
* I leave out of view, for the sake of simplicity, the fact tliat 2-2, 3-3 and 4-4 
would also largely survive ; 1-5, 5-1, and, to a large extent, 4-1, 1-4, 2-5 and 5-2 
would disappear. — T.A.C. 
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Diag. 2. 
