148 NATURAL SELECTION vn 



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 Angrsecum 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 Angrae- 

 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 



