WALTER] 



CLASPING ORGANS IN HYMENOPTERA 



77 



of great service in attaching the hind to the fore wing. At the 

 points where the direction of the stroke changes, particularly at 

 the apex of the eight, the upper loop of which, as Marey states 

 ( 1872, p. 4), is usually very narrow, the wings will have the tendency 

 to move in opposite directions and unclasp, as indicated by the small 

 arrows in the figure. This tendency is restricted to but a moment, 

 and probably not very strong. The wings are protected against 

 the danger of unclasping at this point by the strong recurving 

 of the tips of the distal hooks and strongly projecting margin, 

 of the groove (pi. ix, figs. 22, 23, are ideal examples) ; also the 

 spines at the base of the hind wing and on the convex side of the 

 groove of the fore wing may assist in the prevention of such unclasp- 

 ing, since, acting like rasps, they impede the relative slipping of the 



Direction of Flight 



Down Stroke 



Fig. 21. 



wings. The function of the subbasal hooks is the same as that of 

 the distal hooks ; they play, however, a subordinate role, and in many 

 cases (particularly in the Tenthredinidae) they pass over, morpho- 

 logically as well as functionally, into the marginal bristles, which 

 simply rest against the groove and thereby increase the elasticity of 

 the connection. They are naturally most highly developed in forms 

 with long wings and with the distal hooks greatly approximated to 

 the apex of the wing, as in the Ichneumonidae. The function of the 

 distal hooks of the Tenthredinidae, standing in several rows (pi. ix, 

 fig. 19), is more difficult to explain. Those approximated to the 

 wing margin are so strongly bent outward that the outer ones at least 

 probably also get into the groove under certain circumstances. Their 

 delicacy and elasticity probably enable them to do this (see above). 



