The origin and development of the wings of Coleoptera. 543 



theory of pressure of the haemolymph as a cause of maoy phenomena 

 of insect metamorphosis has been seriously overworked. 



5. Tracheal System of the Wings. 



a) Larval Tracheal System. 



The wings of Coleoptera as far as examined, are all closely 

 associated with the tracheal system even in the youngest stages, and 

 this seems true of every species of insect whose wing development 

 has been studied. In all of the recorded observations the wing funda- 

 ment lies close to the lateral tracheal trunk, from which fine tracheoles 

 pass to the wing disc, or one, usually two, branches of considerable 

 size and length may arise from the longitudinal tracheal trunk and be 

 distributed to the inner side of the disc (PI. 15, Figs. 14 and 16 ; 

 PI. 17, Fig. 29; PI. 20, Fig. 65). In the beetles both of these me- 

 thods of supplying the wings with tracheae are found, but the latter 

 is the more common one. 



In the young stages of L. decemlineata the wing fundament re- 

 ceives two branches from the dorsal tracheal trunk, or more rarely in 

 place of these two single branches, there are two groups of small 

 tracheal tubes which correspond to the single tubes in position, and 

 I believe, in morphological significance. These two centers of tracheal 

 proliferation are undoubtedly the embryonic state of the cubito-anal 

 and costo-radial groups of tracheae which are of constant occurrence 

 in insect wings and which are found in a simple state in the wings 

 of Coleopterous pupae (Comstock & Needham 1899). 



During the early stages of the development of the wing funda- 

 ment the small tracheae described above are able to supply the re- 

 quired amount of air, but when the prepupal stage begins with 

 the rapid growth and changes incident to it the early trachea tion 

 is unable to meet the demands made upon it, and, accordingly, a tem- 

 porary system like that of the Lepidoptera is developed which is 

 functional for a short time and then disintegrates in the pupa. 



In the last larval stage, shortly before the wings begin to expand, 

 the hypotrichal membrane of the dorsal tracheal trunk shows a prolifer- 

 ation of cells at two or more points, usually near the place where 

 the two branches of the trachea to the wing disc arise. This pro- 

 liferation may, however, extend for a considerable distance along the 

 tracheal trunks. In this growth the cells do not become cut off 

 from one another or from the hypotrichal membranes and only partial 



