702 THE PANORPOID COMPLEX, ill., 



Cui a and Cu lb . Likewise also the fork marked x clearly re- 

 presents the archaic position of the fork of R 4 _|_ 5 ; while it is 

 even possible that the vein above it, R 3 may also have pre- 

 served a somewhat smaller fork. Thus we can only conclude 

 also that the forks y and z, belonging to M 1+2 and M 3+4 re- 

 spectively, are the original fox-king's of those veins, and not 

 additions like the smaller terminal twigs. 



Closely allied to the Sisyridae, but less reduced, are the ter- 

 restrial Berothidae (in which the Tfichomatidae may be also 

 included as, at most, a distinct subfamily) . They are, however, 

 specialised by the long series of pectinate descending branches 

 of Cu x in the hindwing. The affinity of this family with the 

 Prohemerobiidae is quite obvious. 



The Hemerobiidae are also a direct offshoot of the Prohemero- 

 biidae, specialised by partial fusion of the main stem, of Rs with 

 R x in the forewing; the result being that some of the pectinate 

 branches of this vein appear to come off from R as separate 

 sectors. Drepanepteryx and allies are the most archaic types 

 of this family (12) . From these, all stages of reduction to very 

 small, highly specialised forms with reduced venation can be 

 easily followed out. 



All the other families of the Planipennia are specialised in 

 one or more directions, and need not be considered here in the 

 construction of the Archetype. 



It is an interesting fact that, in the families Sisyridae, Bero- 

 thidae and Hemerobiidae, in which the cross-vein system is not 

 greatly developed, the same three cross-veins can generally be 

 seen between R 1 and Rs as in the majority of the Megaloptera. 

 Sometimes they are reduced to two in number, as in Text-fig. 

 110. If, now, we turn to the Polystoechotidae (15, fig. 181) 

 we find that, though the number of branches of Rs has greatly 

 increased, the number of cross-veins is still only three or four 

 in this position. It seems fair to conclude from this that the 

 number of cross-veins between these two veins was originally 

 tli re e in both Orders, and that the increase seen in Protohermes 

 and allied genera (Text-fig. 106) in the Megaloptera, and in 

 the great majority of families of the Planipennia, is correlated 

 with the increase in cross- veins in other parts of the wing. 



As all the other families of this Order are specialised in one 

 or more directions, I have omitted them from consideration in 

 the construction of the Archetype. The conclusion we are 



