WALTER] CLASPING ORGANS IN HYMENOPTERA 75 



which form the groove are much thicker than the parts forming the 

 wing proper (pi. ix, most plainly visible in figs. 22 and 23). From 

 the upper convex side above the groove short, pointed, spines arise. 

 These are particularly numerous near the margin. They correspond 

 to 'the spines of a similar kind mentioned in the discussion of the 

 hind wing, and, like these, are directed obliquely towards the apex 

 of the wing (pi. ix, figs. 19 Z 2, 20). Therefore, as Staveley men- 

 tions (i860, p. 135), the margin of the groove appears serrate in 

 surface views. Such spines are chiefly met with in the Tenthredin- 

 idae and Ichneumonidae. In the Vespidae, most of the Fossores, and 

 the Anthophilids these spines are less numerous, more blunt, and 

 often absent altogether. On the other hand, most of the repre- 

 sentatives of the last-named families possess a longitudinal ridge 

 near the margin of the groove generally restricted to the frenal 

 region (pi. ix, figs. 22, 23, Lg), which may be looked upon as a 

 functional equivalent to the spines in other families. 



DEVELOPMENT OF THE HOOKS AND THE GROOVES 



In the autumn of 1905 I obtained some nests of Vespa rufa L., and 

 their pupal inmates offered me an opportunity of investigating the 

 development of the clasping organs, the structure of which has been 

 described above. As unfortunately I did not succeed in obtaining an 

 unbroken series of developmental stages and in this memoir an 

 embryological chapter was not contemplated, I must restrict myself 

 to describing the main features in the development of the distal hooks 

 and the groove as observed by me. The development of the distal 

 hooks commences simultaneously with the brown pigmentation of 

 the eyes and the folding of the wings within the pupal envelope. It 

 is initiated in the region of the frenum. First some hypodermal 

 cells, lying in a row and belonging to this region of the costal 

 vein, become considerably enlarged. In surface views these cells 

 appear as a row of low, small elevations on the upper side of 

 the costal vein. It is possible that the presence of larger frag- 

 ments of fat body, which is always noticeable at this stage, is in 

 some way connected with the formation of the hooks. The cells 

 forming these elevations are the mother-cells of the hooks. From 

 their upper side processes, resembling the necks of bottles, grow 

 out and rise above the upper wing-lamella. These bend over arcu- 

 ately, secrete a chitinous covering, and thus form the hooks. 

 The formation of chitin is first consummated at the distal end 

 of the hook ; whereupon the tapering distal process of the mother- 

 cell withdraws from the end of the hook. In the lumen of the 



