17« 
may be, then ceases to act, instead of being the main agent in all the 
other subsequent changes ?”—(Alfred W. Bennett. Nature, vol. iii., 
A 3 2 -) 
Now, so far as the amount of co-operation required by 
Natural Selection is concerned, we have diametrically 
opposite opinions. Mr. Bates, whose paper is in effect 
an illustration of the Darwinism of Darwin, contends that 
Natural Selection is necessary, but that it plays a com 
paratively small part in the process of transmutation. 
Mr. Wallace, to whom we are indebted for supplying the 
logical nexus which binds together the theory of mimicry, 
in the largest sense of that term, declares that the process 
is very difficult and very protracted. Mr. Bates says:— 
“ I think the facts of similar variation in two already nearly allied 
forms do sometimes show that they have been affected in a similar 
way by physical conditions. A great number of insects are modified 
in one direction by a seaside habitat. I found, also, the general 
colours of many widely different species affected in a uniform way in 
the interior of the South American continent. But this does not 
produce the specific imitation of one species by another ; it only 
prepares the way for it.”—(/>. 508.) 
“ I do not forget that at each step of selection the forms of Leptalis 
must have had sufficient resemblance to an Ithomia to lead to their 
preservation, or at least to prevent their complete extinction ; as, 
however, the two analogues so much resemble each other at the com 
mencement of the process, these steps would not be numerous.”— 
(A 5 12 -) 
Mr. Wallace, to account for the small number of mimics 
in comparison with the models, gives a very different 
account of the action of Natural Selection. 
“ In most of them, favourable variations both of colour, form, 
structure, and instinct or habit, must have occurred to produce the 
perfect adaptation we now behold. All these are known to vary, and 
favourable variations, when not accompanied by others that were 
unfavourable, would certainly survive. At one time a little step 
might be made in this direction, at another time in that. A change 
of conditions might sometimes render useless that which it had taken