554 



THE PAXORPOID COMPLEX, 111., 



Paratrichoptera and Diptera. in which Cn, is a strong, straight 

 vein, without any branches. 



Text-Fig. 40. 

 Stages in the evolution of the 

 pectinate type of first cubitus* 

 from original dichotomic type 

 shown in a. 



In many Planipennia, and some Megaloptera, the original 

 dichotomic forking of Cuj is replaced by a pectinate type of 

 branching, due to additions from the tip inwards. The manner 

 of evolution of this type is shown in Text -fig. 40. 



The Anal Veins. 



These also are dealt with in a special Section (Section v.). 

 I have, however, omitted from that discussion any reference to 

 the probable number of branches of these three veins. A study 

 of the known venational types within the Complex fails to offer 

 us any clear decision on the point, seeing that the branched con- 

 dition of these veins seen in so many Megaloptera and Plani- 

 pennia may be secondarily derived from the simple condition 

 found in the Panorpoidea. I have, therefore, left this question 

 in abeyance, though I have figured these veins in the Archetype 

 of the Complex (Text-fig. 38) as branched, as I think that this 

 is most likely to have been their primitive condition . 



Section iii. The Arculus axd Cubito-mediax Y-Veix. 

 (Plate xxxi., figs. 15-16, and Text-figs. 41-45.) 



The term arculus was originally applied, by writers on the 

 Order Odonata, to the remarkable formation shown near the 



