BY R. J. TILLYAED. 537 



Comstock and Needham applied the test of the pupal or 

 nymphal traeheation to those Orders in which the wings were 

 holotracheate. In the ease of merotracheate types, they were 

 content to obtain results simply by comparative studies of the 

 imaginal wing-venations. Consequently, excellent as is that part 

 of their work which is based upon traeheational studies, their 

 results in the Orders placed in (2) above, as well as in the 

 Hymenoptera, do not carry the same conviction, and errors have 

 unfortunately crept in which might have been avoided by more 

 complete methods . 



After having spent a very large amount of time, during the 

 past three years, upon this research, I have found the following 

 methods yield good results — 



(A) Study of the Pupal Traeheation. This is the essential 

 basis of the study of the wing-venation in the Megaloptera, 

 Planipennia and Lepidoptera. But I soon found, in the course 

 of my researches, that not enough attention had been paid to the 

 age of the pupa studied. In the Megaloptera and Planipennia, 

 unless the pupa is taken fairly early, the wing becomes folded 

 in its sheath, and the courses of the trachea? cannot be followed 

 at all. But, in the Lepidoptera, the wings of older pupae can 

 be withdrawn from their sheaths without damage to the traehea- 

 tion. Thus it frequently happens that results in this Order 

 have been obtained from a study of advanced pupae; yet nobody, 

 so far as I know, has noticed that the traeheation in the ad- 

 vanced pupa may differ very materially from that of the freshly- 

 turned pupa, and may lead to erroneous conclusions. The rule which 

 I followed, and which seems to have only one exception, was 

 this: — Study the pupal traeheation as soon after the formation 

 of the pupa as possible; in any case, remember that it is the 

 freshly-turned pupa that exhibits the most archaic arrangement 

 of the tracheae, while older pupae very often show specialisations 

 towards the type of traeheation preserved in the imago. The 

 exception to be noted is, that, sometimes, in the case of a fusion 

 of veins, both the tracheae underlying the two fused veins do not 

 develop in the pupa, but only one; and that one, as a rule, is 

 the trachea which underlies the more convex of the two veins 

 in question. The other trachea, however, frequently develops late 

 in pupal life, or is to be found in the fused vein of the imago 

 directly after metamorphosis; so that the double nature of the 

 vein is indicated by its carrying two tracheae. 



