148 
NATURAL SELECTION 
VII 
moths ■ and this would be a necessary result from the fact that 
nature ever fluctuates about a mean, or that in every genera- 
tion there would be flowers with longer and shorter nectaries, 
and moths with longer and shorter probosces than the average. 
No doubt, there are a hundred causes that might have checked 
this process before it had reached the point of development 
at which we find it. If, for instance, the variation in the 
quantity of nectar had been at any stage greater than the 
variation in the length of the nectary, then smaller moths 
could have reached it and have effected the fertilisation. Or 
if the growth of the probosces of the moths had from other 
causes increased quicker than that of the nectary, or if the 
increased length of proboscis had been injurious to them in 
any way, or if the species of moth with the longest proboscis 
had become much diminished by some enemy or other un- 
favourable conditions, then, in any of these cases, the shorter 
nectaried flowers, which would have attracted and could have 
been fertilised by the smaller kinds of moths, would have had 
the advantage. And checks of a similar nature to these no 
doubt have acted in other parts of the world, and have pre- 
vented such an extraordinary development of nectary as has 
been produced by favourable conditions in Madagascar only, 
and in one single species of orchid. I may here mention that 
some of the large Sphinx moths of the tropics have probosces 
nearly as long as the nectary of Angraecum sesquipedale. I 
have carefully measured the proboscis of a specimen of Macro- 
sila cluentius from South America, in the collection of the British 
Museum, and find it to be nine inches and a quarter long ! 
One from tropical Africa (Macrosila morganii) is seven inches 
and a half. A species having a proboscis two or three inches 
longer could reach the nectar in the largest flowers of Angrse- 
cum sesquipedale, whose nectaries vary in length from ten 
to fourteen inches. That such a moth exists in Madagascar 
may be safely predicted ; and naturalists who visit that island 
should search for it with as much confidence as astronomers 
searched for the planet Neptune, — and I venture to predict 
they will be equally successful ! 
Now, instead of this beautiful self-acting adjustment, the 
opposing theory is, that the Creator of the universe, by a 
direct act of His will, so disposed the natural forces influencing 
