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cavities, and subject to the pressure of muscular body-walls. 
Hence an insignificant injury may often cause death or imper- 
fect development from the quantity of fluid which is lost. 
“Tt is, I believe, in consequence of these facts that the various 
means of protection in larvee are almost always of a passive 
kind... . Nearly all the means of defence against... 
enemies [other than ichneumons, etc.] are such as tend to 
prevent the larva from being seen or touched, rarely such as to 
be of any avail when actually attacked. There may be various 
changes in the mode of defence, but the object is always the 
same—to leave the larva untouched, a touch being practically 
fatal.” * 
Let us consider for a moment the mental operations involved 
in the act of profiting by experience. Consider, for instance, 
Mr. A. H. Hamm’s interesting observation—since abundantly 
confirmed by the testimony of many naturalists—that the vast 
majority of the individuals of Hybernia leucophexaria rest with 
the body horizontal, thus bringing the lines of the wings into 
parallelism with the dark shadows in the vertical cracks of the 
oak-bark.+ Anindividual which adopted a different attitude 
and rested so as to cause the main lines of its pattern to cut 
the main lines of its environment might indeed escape by 
flight ; but can any one really believe that a moth, or any of 
the ancestors of moths, could associate the special disturbance 
and danger to which it had been exposed with the special 
attitude it had assumed, and would as a result of that associ- 
tion begin to make changes in its attitude? It is easy to 
speak of improvement by experience, perhaps easy to think of 
the progress of an insect’s education under the sternest of 
teachers: easy so long as we confine ourselves to generalities. 
Attempt to picture the process in a definite case, and apply it, as 
I have done, to account for the growth of some special protective 
adaptation, and it is instantly borne in upon us that we are 
placing on insect psychology a load it is altogether unable to 
bear. 
The Cocoon-making Instinct.—There are however number- 
less examples in which it is impossible that improvement could 
* Trans. Ent. Soe., London, 1885, pp. 321-323. 
+ Proc. Ent. Soe, Lond. for March 19, 1902, p. xv. 
