57 
r i , . SEXUAL SELECTION IN LEPIDOPTERA. 
* ha '’ e alread y ( British Xoctuae and their Varieties, vol iii p xvii) 
confess*1 : hnf U f 1 86 ectl0 , n Jn lts application to Lepicloptera, and, I must 
££ ZTl fe# V mal1 < bnltCtfi 
inTheL^pidopta 8 ” 1 <l0 “ 0t th “ k Suoh M™>» «*. 
■j. granted the existence of sexual selection, then I fail to see how 
it te ds to the development of specific characters, useful or useless 
To me sexual selection appears only as another phase of the ueneral 
and chiosin- of'th S f elect J° n ’ and ’ althou gh I can see that the picking 
choosing of the females may stamp a character already in exist¬ 
ence in the males, more markedly on the race, I fail to see how it can 
ThaHhV? 7 T V Char m ter for fchis Active process to act upon 
That the females would, as a race, continue to pick males that 
lhat had ceased t0 be of ^ 
T 1 ISOLATION FIXES CHARACTERS ALREADY FORMED. 
i d ° i i 1 . 1 . that . lsolati °h can beget specific characters. There 
rflctP^t 130 d ° Ub f th f tends t0 fix ’ h y natural selection, such cha¬ 
racters as are already m process of settlement. The tendency to close 
“ di ng, the more constant character of the environment to 
ch the species is subjected, and other similar causes tend to define 
h! ^ ara ? te f s , more «*«Ply when a species is strictly isolated from 
the ancestial form. I have already shown how isolation need not be 
a physical isolation like the separation of an island from the adjacent 
bUt th L fc t ]? e . enier g euc e of closely allied species at different 
tunes of the year, by flying at different times of the day or night, or by 
being restricted to different food-plants of local habit, might be just 
as potent as separation by physical barriers. 
LAWS OF GROWTH. 
v/i- urAuuin. 
Nor can the laws of growth originate specific characters. The 
L7Q nr rrrn ruf-h if o l _ , i . 
laws of growth, it appears to me, must be applied to actual existent 
parts of an organism, and, until some nervous or other exciting cause 
has been stimulated to bring about a modification, I do not see how 
the lawsof growth can influence any structure or organ. It appears 
to be the case that, only when other causes have brought about 
changes useful to the species, these laws can have any action at all. 
SUMMARY OF EFFECTS PRODUCED BY CLIMATE, FOOD, ETC. 
It will be thus seen that I doubt entirely the power of climate 
food, sexual selection, isolation and laws of growth, to produce specific 
characters at all, whether useful or useless. The modification of parts 
necessary to bring about a new specific character cannot be originated 
