The cocoons of bifida are spun in the autumn, but the attack 
did not take place for several months. The example is 
probably typical in this respect. The procryptic preparation 
of the autumn is the adaptation by which the average 
numbers of the species are kept up in spite of ceaseless bark- 
hunting during the months when the trees are leafless and 
food is searce. The Lamarckian interpretation fails to 
account for the cocoon-making instinct for two very sufficient 
reasons : first, a chrysalis is incapable of learning by experience 
how to improve anything,—even more obviously incapable 
of learning concerning a structure which it never makes. 
Secondly, however intelligent a chrysalis may be, the experience 
itself is of such a nature that its stores of learning cannot be 
handed down to posterity.* 
If the Lamarckian interpretation of the cocoon-making 
instinct must inevitably fail, as I think we shall agree it must, 
what is there to put in its place? Those who believe in the 
efficiency of Natural Selection in evolution will probably 
regard the instinct of building these beautifully-adapted 
structures as the outcome of countless generations during 
which the attacks of enemies have been, on the whole, more 
successful against the products of less perfected instincts and 
less so against those of the more perfected. They will further 
suppose that the increasing perfection in instinct has acted 
selectively on enemies, sharpening their faculties, until, by 
action and reaction, the present high level of constructive 
skill has been reached, and is maintained. 
The Instincts of the Hymenoptera.—No discussion of instinct 
would be in any way complete without a consideration of the 
most wonderful examples of all, viz. those manifested by the 
Hymenoptera. The instincts of the Fossorial Aculeates in 
providing for their larve, 
studied with all the sympathy of 
a born naturalist and described by a master of style,—have 
erroneously given as the year of issue instead of 1893. Some of the 
later sentences of the same communication are also quoted with slight 
modification on the present occasion. 
* This argument also is briefly stated in the ‘Proc. Boston Soc. Nat. 
Hist.,” vol. xxvi, 1894, p. 391, and quoted in ‘‘The Zoologist,” Dec. 1900, 
pp. 951, 552. 
