( lix ) 
to state the case with any bias on the present occasion. 
Now the experiments of Poulton have shown that this 
colour variabiHty is of very much more frequent occurrence 
than was even dreamt of in 1873, and his facts have, in the 
main, been substantiated by the independent observations of 
many other experimenters. And it turns out also that the 
mechanism of the process is not even the simple assimilation 
of colouring-matter from the food-plant, excepting in the case 
of green caterpillars, in which it has been shown that 
chlorophyll in a modified form passes into the blood. The 
colour variability of caterpillars and pupge in response to 
the external stimulus exerted by coloured surfaces, as estab- 
lished by these experiments, has brought us face to face with 
a fundamental problem in insect physiology, the solution of 
which we are anxiously awaiting. The mere possibility of 
being able to state the problem in its present form — apart from 
any question of the adaptive value of the colouration — is a 
step forwards ; is an incentive to further experiment, and 
this is the legitimate end and aim of all scientific specu- 
lation. 
Were I to attempt, however, to pass from what has 
already been accomplished to that which is yet awaiting 
investigation — to the questions which rise on all sides as 
pressing for solution, there would be no limit to this address. 
In view of the splendid opportunities afforded by insects for 
treatment as living organisms capable of revealing natural 
laws by skilled experimental research, is it not pardonable 
if we sometimes give way to the unphilosophic thought that 
the possession of chitinous exo-skeletons by these creatures, 
whereby they lend themselves so admirably for preservation 
as cabinet specimens, is an arrangement expressly designed 
for the retardation of entomological science ? The scientific 
workers at living insects in this country are deplorably few 
as compared with those who devote themselves to cabinet 
entomology. The one great desideratum of modern biology 
is an experiment station where protracted observations can 
be carried on year after year on living animals, each set of 
experiments prompted by hypothesis and with the definite 
object of answering some particular question in relation to 
