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process has often been described. It has been pictured 
over and over again by the imagination of scientific 
theorists, but in the general terms of faith rather than with 
convincing details of demonstration derived from the 
observed modification of a given group of individuals. 
Yet such a successful experiment ought to be possible if 
the theory were in accordance with the facts of nature. 
I.—COLOURS WHICH CONCEAL. 
“ The shadow cloaked from head to foot.” 
—Tennyson. 
We are told that there are some organisms so con 
cealed by their colour that they are only to be recognised 
by the shadows which they cast. It is the extreme illus 
tration of a very frequent phenomenon which is supposed 
to secure the safety of the individual and the survival of 
the species. We have now to ask whether this phenome 
non has been brought about by Natural Selection, and 
whether it has been produced in such a manner that it 
affords the most favourable illustration of the action of 
that reputed law of nature. 
On the threshold of the subject, we must pause to con 
sider whether concealment by colour affords that perfect 
immunity from attack which is generally attributed to it. 
Whether a given animal is visible or invisible is very 
much a question of experience or inexperience on the 
part of the spectator. “We must get out of the way,” 
says Mr. Beddard, “of judging instances of this kind 
from the human standpoint. The most acute observers 
among us are dull compared with uncivilised man and 
many animals.”* He makes this remark apropos of the 
Animal Coloration, p. uo.