THE WINGS OF HYMENOPTERA 



377 



C^Ii^M 



gastra occurs. The other two figures, e and/, represent this part of the 

 wing in two members of the suborder Chstogastra, Pelopazus and Apis 

 respectively. 



In Macrocephiis satyr us (Fig. 397> a) ^he direction of both the basal part 

 of the radial sector and of the radial cross-vein is oblique; and the 

 radial cross-vein has the 

 appearance of being a longi- 

 tudinal vein branching from 

 the stigma, and not that of a 

 cross-\'ein, a foreshadowing of 

 its function in more special- 

 ized forms. 



In Janus cyuoshati (Fig. 

 397, h), a short section of the 

 base of the radial sector near 

 the stigma has faded out. In 

 Janus abbreviatus (Fig. 387, 

 c), a longer section of this vein 

 is lacking. And in Oryssiis 

 abieiinus (Fig. 397, c?),all of 

 the radial sector proximad of 

 the radial cross-vein is lack- 

 ing; and this cross-vein 

 appears to be the base of the 

 radial sector. Thus is fonned 

 a serial vein, consisting of the 

 radial cross- vein and the rem- 

 nant of the radial sector, 

 which has the appearance of 

 a simple xem. This is the 



m cu 



Fig. 397. — The switching of the base of the 

 radial sector (From MacGillivra}')- 



condition that exists in all of the Chstogastra and is ilhistrated by PelopcBus 

 cementarius (Fig. 397, £^) and Apis mcllifica (Fig. 397,/)' 



Figures 398 and 399, representing two entire wings, will illustrate two 

 stages in this switching of the base of the radial sector. In Janus abbrevia- 

 tus (Fig. 398), the atrophy of the section of the radial sector between the 

 point where it is joined by vein r-m and the stigma has begun; in Odon- 

 taulacMS editus (Fig. 399) the atrophy of this part of the radial sector is 

 complete. 



Correlated with the series of changes just described are changes in some 

 adjacent parts that merit description, and which were also pointed out by 

 Dr. MacGillivray. The parts refeiTcd to are the radio-medial cross-vein 

 and that part of the radial sector that lies between the radio-medial cross- 

 vein and the radial cross- vein. 



