422 BIU J. LUB130CK ON TUE OKIQIN OF INSECTS. 



On the Origin of Insects, By Sir Joun Lubbocb:, Burt. 

 [Bead November 2, 1871.] 



The metamorphoses of this group have always seemed to me one 

 of the greatest difficulties of the Darwinian theory. In most cases 

 the development of the individual reproduces to a certain extent 

 that of the race ; but the motionless, imbecile pupa cannot repre- 

 sent a mature form. Fritz Miiller considers that the wingless 

 Blattidss probably most closely represent the original insect 

 stock J Hackel is inclined rather to the Pseudo-Neuroptera. I 

 feel great difficulty in conceiving by what natural process an 

 insect with a suctorial mouth like that of a gnat or butterfly 

 could be developed from a powerfully mandibulato type like the 

 Orthoptera, or even from the Neuroptera. M. Brauer has re- 

 cently suggested that the interesting genus Campodea is, of all 

 known existing forms, that which probably most nearly resembles 

 the parent insect stock. He considers that the grub form of 

 larva is a retrograde type, in which opinion I am unable to 

 concur, tliough disposed to agree with M. Brauer on the first 

 point. M. Brauer, in coming to this conclusion, relies partly 

 on geological considerations, partly on the fact that larva) 

 more or less resembling Campodea occur among widely different 

 groups of insects. I think there are other considerations which 

 offer considerable support to this view. No one, so far as I 

 know, has yet attempted to explain, in accordance with Mr. 

 Darwin's views, such a life-history as that, for instance, of a 

 butterfly, in which the mouth is first mandibulate and then suc- 

 torial. A clue to the difficulty may, I think, be found in the 

 distinction between developmental and adaptive changes, to which 

 I called the attention of the Society in a previous memoir. The 

 larvao of insects are by no means mere stages in the development 

 of the perfect animal. On tlie contrary, they are subject to the 

 influence of Natural Selection, and undergo changes which have 

 reference entirely to their own requirements and condition. It 

 is evident, then, that, while the embryonic development of an 

 animal in the egg gives an epitome of its specific history, this is 

 by no means the case with species in which the immature forms 

 have a separate and independent existence. Hence, if an animal 

 when young pursues one mode of life, and lives on one kind of 

 food, and subsequently, either from its own growth in size and 

 strength, or from any change of season, alters its habits or food. 



