xxxiii, '22] ENTOMOLOGICAL NEWS 7 



While admitting that, in most cases, the precedent larval 

 tracheation may be profitably studied for the purpose of deter- 

 mining the homologies of the imaginal veins, it should be evi- 

 dent to everybody that larval wing-tracheation may be just as 

 much subject to change, along its own evolutionary line, as is 

 the imaginal wing-venation, or any other structure. In his 

 work on the Odonata, Needham seems to have worked along 

 the lines of assuming that, in all cases, the tracheation was to 

 be relied upon to show absolutely the line of evolution of the 

 venation. It is another instance of an attempt, of which there 

 have been many, to apply Haeckel's Biogenetic Law in its 

 entirety, without taking into account the possibility of larval 

 structures, such as the wing-tracheation, undergoing lines of 

 evolution of their own, so that they, in certain cases, may be- 

 come far more highly specialized than the corresponding 

 imaginal structures. It is certainly possible to prove, from the 

 fossil record, that Needham's supposed bridge-vein was never 

 formed backwards as a bridge-vein, but was always the 

 basal portion of a strongly formed main longitudinal 

 vein arising from M3 (or sometimes Ml +2, as in most 

 recent forms) close to the point of separation of these 

 veins. This proof I propose to give in another part 

 of these researches, which will deal entirely with fossil 

 forms. Meanwhile, for the further elucidation of the 

 problem, I now propose to denote this entire vein by the nota- 

 tion Ms, as I have previously done for the Zygoptera. Logi- 

 cally, if we admit five branches of M, they should be called 

 Ml, M2, M3, M4 and M5, respectively, instead of Ml, M2, 

 Ms, M3 and M4, as at present ; this I have already pointed out 

 in a previous paper. 3 But, as a matter of fact, we have 

 not come down to the true solution of the whole problem yet, 

 and so I propose to let the notation Ms stand, seeing that it 

 is at any rate now proved that this vein was originally a true 



branch of M. (To be continued) 



EXPLANATION OF PLATE I. 

 Fig. 1. Uropctala chiltoni Till., penultimate larval instar, tracheation 



of hindwing. (x 13.) 

 Fig. 2. Uropctala chiltoni Till., penultimate larval instar, basal third 



of hindwing more highly magnified, to show tracheation. (x 45.) 

 Fig. 3. Uropctala chiltoni Till., antepenultimate instar, forewing, 



region of nodus and oblique veins, (x 38.) 



3 Tillyard, R. J. "The Panorpoid Complex. Part 3: The \Vin- 

 Venation." Proc. I.inn. Soc. N. S. W., 1919, xliv, pt. 3. pp. 533-718. 

 (See pp. 555-9 and text-fig. 41.) 



