48 
juriously under the new conditions. Given these conditions, and the 
injury will result in extermination, unless some structural or functional 
modification be developed in the species, which will enable it to 
combat the disabilities under which it now lives, and, in time, to 
succeed under the new conditions. We have already seen that a 
recent change in the environment of certain Lepidoptera has resulted 
in the development of a maximum of black scales, so that the colour 
of the insect may respond to its new environment. We have also 
seen that this change of colour is simply a change in the proportion 
of the black scales (always present in the species) developed. The 
change then must take place by the modification of the different 
variable factors that play around, what we may term, the “ mean” of 
any structural part of the insect; and, it must be evident that from 
these variable factors alone, can utility obtain the materials which it 
moulds into those lines, which will fit the species to its new environ¬ 
ment. Survival of the fittest in the required direction (or directions), 
goes on year by year, and thus the species is maintained under the 
new conditions. 
Little further insight is needed to see that more than one modifi¬ 
cation may be necessary, and that under a complex series of change, 
divergent races might be formed, each specially suited for success 
in different directions, whilst the original type of the species might 
become extinct. 
In this way we obtain the beginnings, as it were, of new species, 
which may take a vast period of time before they become thoroughly 
differentiated from each other. The more rapidly and sharply certain 
peculiarities separate them, especially peculiarities of the genital 
organs, the more rapidly would their complete separation as species 
be brought about. 
SPECIALISATION OF GENITAL ORGANS DOES NOT NECESSARILY ACCOMPANY 
OTHER SPECIALISATIONS. 
There appears to me, however, to be no reason whatever why 
changes of the genital organs should take place under changing con¬ 
ditions of environment, such as those just suggested, nor why changes 
in the genital organs should accompany other changes, necessary for 
greater speed, better concealment, or other habit now assumed to be 
a matter of necessity to the species. It is evident, that the safety of 
insects depends primarily upon colour (protective or warning), speed, 
nauseous excretions, development of fascicles of hair in place of 
simple tubercles, waving flagella, osmateria, discharges of acid and 
gaseous matters and similar factors, rather than on changes, either in 
structure or function, of the internal organs. All, or any, of the 
various changes just enumerated may be effected without the slightest 
change in the structure of the genital organs, and hence it is possible 
for new species to be developed with distinct and conspicuous external 
characters, either in the imaginal, or pupal, or larval, or oval stages, 
or in all, or any, of these stages, without any very great modification 
being necessary in the genital organs. These external characters may 
be most marked, and, in evory respect, specific, as we understand the 
term. Yet the possibility of successful pairing and the production of 
fertile ova, between the supposed allies may always be present. 
VARIATION IN GENITAL ORGANS. 
That thoro is usually some well-marked difference prosontod by the 
