1870— 1882] METAMORPHOSIS 331 



Campodea} I never reflected much on the difficulty 2 which Letter 244 

 you indicate, and on which you throw so much light I have 

 only a few trifling remarks to make. At p. 44 I wish you 

 had enlarged a little on what you have said of the distinction 

 between developmental and adaptive changes ; for I cannot 

 quite remember the point, and others will perhaps be in the 

 same predicament. I think I always saw that the larva and 

 the adult might be separately modified to any extent. 

 Bearing in mind what strange changes of function parts 

 undergo, with the intermediate state of use, 3 it seems to me 

 that you speak rather too boldly on the impossibility of a 

 mandibulate insect being converted into a sucking insect ; ' 

 not that I in the least doubt the value of your explanation. 



conversational variant of the Laputan comparison which gave rise to the 

 passage in the Descent of Man (see Letter 130). 



1 " On the Origin of Insects." By Sir John Lubbock, Bart. Tourn. 

 Linn. Soc. (Zoology), Vol. XL, 1873, PP- 422-6. (Read Nov. 2nd, 1871.) 

 In the concluding paragraph the author writes, "If these views'are 

 correct the genus Campodea [a beetle] must be regarded as a form 

 of remarkable interest, since it is the living representative of a primaeval 

 type from which not only the Collembola and Thysanura, but the other 

 great orders of insects, have all derived their origin." (See also Brit. 

 Assoc. Report, 1872, p. 125— Address by Sir John Lubbock; and for a 

 figure of Campodea see Nature, Vol. VII., 1873, P- 447-) 



2 The difficulty alluded to is explained by the first sentence of Lord 

 Avebury's paper. "The Metamorphoses of this group (Insects) have 

 always seemed to me one of the greatest difficulties of the Darwinian 

 theory ... 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 mandibulate type like the orthoptera, or 

 even from the neuroptera ... A clue to the difficulty may, I think, be 

 found in the distinction between the developmental and adaptive changes 

 to which I called the attention of the Society in a previous memoir." 



The distinction between developmental and adaptive changes is 

 mentioned, but not discussed, in the paper " On the Origin of Insects " 

 (loc. tit., p. 422); in a former paper, "On the Development of Chloeon 

 (Ephemera) dimidiatum (Trans. Linn. Soc, XXV, p. 477, 1866), this 

 question is dealt with at length. 



3 This slightly obscure phrase may be paraphrased, " the gradational 

 stages being of service to the organism." 



4 "There are, however, peculiar difficulties in those cases in which, as 

 among the lepidoptera, the same species is mandibulate as a larva and 

 suctorial as an embryo" (Lubbock, "Origin of Insects," p. 423). 



