304 THE PANORPOID COMPLEX, i., 



the typical manner. Of the New Zealand Porina nmhracnlata, 

 Mr. Philpott writes, "the jugum is so small as to seem worthless 

 as a coupling in the manner of finger-and-thumb." 



Thus we see that there is a considerable diversit\" in the form 

 and function of tlie jugimi, as developed in the Hcpialklfc. 



The discussion as to how the highly specialised jugum of the 

 Hefialidcv is related to the jugo-frenate type of coupling-appa- 

 ratus found in the Microptpryciicht' is best left until we have 

 dealt with the Heteroneura. 



ii. Suborder HETERONEURA. 

 A. Frenate Types. (Plate xxx., figs.6-8, and Text-figs. 13-1 6). 



Mey rick's excellent definition of the frenate tj^pe has already 

 been quoted on p. 296. We ma)^ now profitably study, in more 

 detail, the difi'erences between the female and male types. 



These differences are clearly correlated with differences in the 

 power and frequency of flight. In those forms in which the 

 female flies but little, the frenulum remains small, and composed 

 of a number of separate bristles, while that of the strongly-flying 

 male may be very large and strong. But in other forms, in 

 which both sexes fly almost equally well, the frenulum of the 

 female may be almost as strongly formed as that of the male, 

 though never consisting actually of a single bristle. 



Text-fig. 13. 

 Wing-eoupling apparatus of Hippotion i^cro/a {Boisd.), 9 , showing fren- 

 ulum of eight separate bristles, and retinaculum of hairs arising from 

 cubitus (C'?0; viewed from beneath; ( x 16): h/, humeral lobe. 



Text-fig. 13 shows the frenulum of a female Sphingid {Hippotion 

 scrofa Boisd.). The bristles composing it are eight or nine in 



