xxxiii, '22] ENTOMOLOGICAL NEWS 47 



with an ancestral form of this type, the true Anisoptera began 

 with forms in which the point of origin of M2 became fixed 

 close under the nodus. The small trachea beneath the nodus, 

 arising from R, and supplying the subnodal vein, must next 

 have grown out as a very slender branch beneath .1/1 and M2, 

 just beyond their point of union, and must have at last found 

 its wav down to the level of Ms at about the middle of the 



j 



long bridge. There being no trachea supplying the long bridge, 

 it is not difficult to see how this new trachea came to supply 

 its distal half. With a very slight increase in the development 

 of this trachea, we get the stage represented in the ante- 

 penultimate instar of the larva of Uropetala, in which the 

 calibre of the new tracheal outgrowth is still much smaller 

 than that of Ms. Further increase in calibre would give us 

 the present condition in the last instar of Pctaluridae, in which 

 the trachea from the subnodus underlies the basal oblique vein 

 0, and supplies also that portion of Ms between O and O'. I 

 would suggest that the notation Rs for this trachea should be 

 definitely abandoned. As it is a tracheal outgrowth from R 

 below the nodus, it should be called the subnodal trachea, 

 while the notation Ms should be kept for the whole vein. If it 

 is desired to distinguish the three portions of the vein Ms in 

 Pctaluridae, we might speak of the bridge or basal portion, the 

 subnodal or middle portion, and the distal portion, respectively. 



Thus we see that the Pctaluridae stand as the oldest type 

 extant within the Anisoptera, possessing tzuo tracheal special- 

 izations in the region of Ms; one, indicated by 0' , being derived 

 from Anisozygopterous ancestors, and being homologous with 

 that seen in the Lestidae and Epiophlebiidae; while the other, 

 indicated by 0, is peculiar to the Anisoptera, and is to be con- 

 sidered as of later origin. 



(E) If we examine the Cordulegasteridae, which show 

 affinity with the Pefaluridac on the one hand and with the 

 Aeschnidae and Gotnphidae on the other, we find occasional 

 specimens in which the two oblique veins of the Pctaluridae 

 are present. But, in most cases, only the basal oblique vein 

 is present, with a short bridge-vein. Thus, in this family, we 

 see the dying out of the original tracheal specialization indi- 



