"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.

cit., page 422); in a former paper, "On the Development of Chloeon (Ephemera) dimidiatum ("Trans.

Linn.

Soc." XXV.

page 477, 1866), this question is dealt with at length.) I have only a few trifling remarks to make.