xxxiii, '22 j ENTOMOLOGICAL NEWS 259 



and the delicate tracheae contained in them are suhjected to no 

 strain or pressure of any kind and there is practically no dan- 

 ger of the tracheae being displaced from their normal courses. 

 The figures are all from drawings made with the aid of a 

 camera lucida, for it was found that the earlier stages, such ns 

 those in which the wings were less than 0.5 mm. in length, 



o O 



could not be photographed, since the high magnifications neces- 

 sary make it impossible to get all the tracheae in focus together. 

 In the wing measurements given, the term "length" is used to 

 indicate the distance between the mid-point on the line of 

 articulation of the wing with the thoracic tergum and the 

 extreme tip of the wing. 



In A mi. r, the smallest larvae posse-sing wing rudiments 

 which I was able to obtain were 9 to 10 mm. in length. The 

 wings of these larvae were 0.2 to 0.22 mm. long; three such 

 wings, from different larvae, are represented in figs. 1-3. The 

 shortness of these wings compared with their width at base 1 and 

 the less definite arrangement of their tracheae make it imme- 

 diately apparent that we have to do with a much earlier stage 

 in the development of the wing than in the case of the earliest 

 stages represented by Needham's figures or by Tillyard in his 

 text fig. 3. 



In comparing the wings in figs. 1-3, it is noted that there is 

 considerable variation, that there is not a single trachea which 

 is exactly alike in all three figures but that each may vary in 

 the number of its branches and that their arrangement gives 

 but little hint as to the manner of their disposition in the adult. 

 We also note that additional tracheae may often appear between 

 the costa and the subcosta ; in fig. 2 there are two such tracheae, 

 in fig. 1 there is one. I am confident in assuming that in all 

 cases the extra tracheae are between C and Sc and that .!/ is 

 always adjacent to R, for I have never found, at any stage in 

 . Ina.v, any indications of extra tracheae inserted between A' and 

 M. Thus I have found, as Needham did, that in the earliest 

 stage in the development of the wing there are six principal 

 tracheae. The additional tracheae of which there mav he one 

 or more inserted between C and Sc, may persist through late- 

 mstars but always remain small and are of no importance. 



