INSTINCT AND HABIT. 
9 
better sense organs ; all crystallises down to a specialised form with 
fixed instincts. So too, for instance, with parasitic insects, the new 
habits imply new structure, the petiolate body and the ovipositor are 
developed to lay the eggs, and with the necessity for flying by day comes 
warning colouring and unpleasant taste or odorous glands, since birds 
are developed also and are taking to eating insects. Consider a Sphegid 
catching live insects, paralysing them, laying them up for its young ; 
imagine the development of such forms, the gradual acquirement of 
more and more perfect structures, and with them of more and more fixed 
instincts till we have the perfect insect, with intensely modified life 
history, with fixed and complex structure and with nearly all plasticity 
and power of change gone. 
This is the point I wish to make ; we are now at a stage in 
the earth’s history when competition has produced an amazingly 
complex number of forms of insect life, which adapted themselves to 
every condition of life but that in saltwater, which have, by the im¬ 
provement of more and more perfect forms, become increasingly 
complex, specialised and fixed ; variation, except in each special 
direction, makes for destruction; from the increasing competition 
plasticity is gone, the forms are fixed and unalterable, and what may 
once have been forms of active mentality implying some choice, some 
volition, are now fixed instincts, crystallised reflex and, possibly, 
voluntary actions. It is true that all are not equally complex or special¬ 
ised, but I believe it to be true that almost all, simple or complex, are 
fixed, are no longer alterable except so minutely and so slowly that we 
can no longer see it. It is questionable whether there is any form with 
which we could people a part of the earth, say an island, that was abso¬ 
lutely devoid now of insect life, and in which we could see this process 
of differentiation and specialisation take place, but could we find such a 
form, could we give it the same free field and let it multiply and increase, 
we should get a similar differentiation and an ultimate specialisation of 
equally fixed forms. 
The student may read this for himself at greater length in text¬ 
books of palaeontology, geology and evolution; he must realise it if he 
is to grasp the meaning and origin of the forms and habits of insects; 
and in no other group is it so marked as in insects ; when we consider 
the abundance of forms of life in the insect world, their absolutely 
