419 
‘guides’ and ‘path-finders,’ as they invariably lead to 
the nectaries.” 
“ If the theory be true, which I am endeavouring to maintain 
throughout this book, all these effects are simply the direct results 
of the insects themselves. The guides are always exactly where the 
irritation would be set up ; and I take them to be one result of a 
more localised flow of nutriment to the positions in question.”— 
(The Structure of Flowers, p. ry8.) 
Those causes of modification which can co-operate with 
transforming influences are also useful. A structure of 
co-ordinated parts is obviously useful, and the correlated 
variation which assists in transforming one co-ordinated 
structure into another is obviously useful. For although 
this may sometimes act in a way which does not seem of 
any use, yet, taken on the whole, it must be of immense 
value ; for a large increase in the growth of the horns 
would be an unbearable burden if correlation of growth 
did not come to the aid of the animal so modified. 
In bi-lateral organisms, correlation of growth gives a 
balance and equipoise, the absence of which would be 
most disastrous. And if we are permitted to regard co 
ordination of structure as the result of this principle, its 
value and utility can be doubted by no one. 
It is quite conceivable that other changes associated 
with reproduction may also prove useful. Take, as an 
illustration, the case of the ancon ram. Here you have a 
considerable divergence from the normal structure, effected 
at one birth, and which was useful from the point of view 
of domestication, because the animal with short legs could 
not jump so well as the others, and consequently could be 
kept in bounds by lower, and therefore less expensive, 
fences. It is quite conceivable that, in some cases at any 
rate, a similar use might be found for an organism sud 
denly developed in nature. By such a modification, the