WALTER] CLASPING ORGANS IN HYMENOPTERA 71 



not fully colored specimens cut out of pine wood, I found the bottom 

 of the pan perforated ; but in the center in every case there was dis- 

 tinguishable a differentiated bordering layer between the pan-cavity 

 and the matrix of the costal vein (pi. x, fig. 27, Gr). In older ani- 

 mals also the bottom of the pan sometimes appears centrally per- 

 forated in cross-section, but in this case the edges of the opening 

 are sharply broken, and clearly indicate that the missing piece of the 

 bottom has broken away in sectioning, on account of the well-known 

 brittleness of older chitin (pi. x, fig. 28). This difference between 

 young and fully developed specimens shows that the closing of the 

 chitinous pan is effected by chitin secreted after the formation of the 

 wing-lamellse. The pan is about 37 microns wide. Its outer opening 

 is covered, like a drum, by a fine membrane, which appears as a con- 

 tinuation of the outer layer of the upper wing lamella (pi. x, fig. 28, 

 Me). Centrally this membrane incloses the hook, the basal part of 

 which projects about 15 microns into the cavity of the pan. The hook 

 has a diameter of 22 microns. It is not thickened at the base. The 

 lumen of the hook (pi. x, fig. 28, I) terminates basally with a funnel- 

 shaped extension. Numerous fine, transparent chitinous threads aris- 

 ing from the inner wall of the pan, attach themselves to the basal end 

 of the hook (pi. x, fig. 28, F) and hold it fast. From the central 

 portion of the bottom of the pan no such threads arise. This con- 

 tributes to the ease with which this part of the pan is broken away 

 in sectioning. 



A type of insertion wholly different from this is found in the 

 Anthophilids. In these Hymenoptera the wall of the costal vein is 

 extremely thick. Sometimes the two lamellae forming it, of which 

 the upper is always considerably the thicker, touch each other, so 

 that the vein lumen entirely disappears (pi. x, fig. 30). It is perhaps 

 on account of the strength of the walls of the costal vein, that the 

 mode of inserion of the hooks is much less complicated in the Antho- 

 philids than in the Siricids. I particularly examined the distal clinch- 

 ing hooks, peculiar to the Anthophilids, in Apis melliiica L., Bombas. 

 terrestris Latr., Bombus lapidarius Walck., and Megachile ericetorum 

 Lep. The upper lamella of the costal vein, very stout in all the spe- 

 cies of this family, forms prominent ring-shaped thickenings round 

 the bases of the distal hooks (pi. x, fig. 30, R), which are homologous 

 with the elevated rings of the Tenthredinids. The prominences are 

 centrally perforated by conical tubes into which the basal ends of the 

 hooks are inserted. The considerably thickened basal end of each 

 hook fits closely into this tube, so that the hooks appear firmly em- 

 bedded in the costal vein (pi. x, fig. 30). The distal hooks of 



