238 Journal New York Entomological Society. [Voi. xii. 



(1767), while the beginning of our accurate knowledge of the manner 

 of their development was made by Weismann (1864-6). Since his 

 time there have been many workers in this field, but most of them 

 have worked with the Lepidoptera and Diptera — orders in which the 

 wing development is of a very complicated type, while on the Hetero- 

 metabola and the more generalized of the Holometabola as the Cole- 

 optera and Neuroptera, much less has been done. The only extended 

 accounts of the development of the wings in the Coleoptera are those 

 of Comstock and Needham (1899), Kruger (1899), Needham (1900) 

 and Tower (1903). 



In this paper I have traced in detail the development of the wings 

 of two species of Scolytidae or engraver beetles, Toniicus plastograpJius 

 and Dendroctonus valens and have added some observations made 

 on the development of the wings of a number of other beetles, the 

 complete history of which I was unable to obtain. I have dealt only 

 with the development of the wings in the larva, as it is probable that 

 there is nothing in the pupal development of the wing that differs 

 greatly from the accounts of Tower and others, or likely to have any 

 bearing on the origin of wings. The second part of the paper is de- 

 voted to a discussion of the several theories that have been advanced 

 to account for the origin of the wings of insects and the bearing that 

 my observations have on the subject. 



I. The Life History of Tomicus pla stogeafhus Leg, and 

 OF Dendroctonus valens Hopk. 



Both these beetles belong to the family Scolytidae and in some 

 localities in California are so numerous that they do considerable 

 damage to the Monterey Pine, on which they both feed. 



The burrow made by the adult T. plastographus is some six inches 

 in length and is three-branched, having something the shape of a Y, 

 the entrance being at the intersection of the branches, one of which 

 is considerably shorter than the others. The eggs are laid in little 

 pockets along each side of the burrow and are tightly packed in with 

 little chips of wood. In warm weather the eggs hatch in about one 

 week. The larva bores a tunnel out at right angles to the parent 

 gallery and becomes full grown in about two weeks. Pu]Dation takes 

 place in a cell at the end of the larval gallery and lasts about one 

 week ; so that a full life cycle is passed through in about four weeks. 

 Breeding goes on continually throughout the year in this locality, but 



