1913.] 183 



Chrysids are not Aculeates, and one may not reason from the 

 latter witli much certainty, not only because Chrysids are not Aculeates, 

 but because the female Chrysis has no duties towards her offspring 

 beyond oviposition. It is further the case that the dentate margin 

 in Chrysis is a specific and not a sexual character, i.e., it is nearly 

 identical in both sexes of the species that possess it. The dentate 

 margin is not of a terminal segment. The segment carrying the teeth 

 is the last visible one, but so, only the third visible segment of the 

 abdomen, probably really the fourth. 



Taking all these circumstances and some others into consideration, 

 the theory of these spines that seems to me probable is, of course, very 

 hypothetical, and can only claim acceptance in the absence of a 

 better. In the Ent. Mo. Mag. of 1869 and 1870, I gave some notes 

 on the habits of the Chrysids parasitic on Odynerus spinipes. Chrysis 

 neglecia substitutes her own egg for that of the wasp, laying it whilst 

 the cell is still open and even before the tale of green grubs for sub- 

 sistence of the larva is complete. Chrysis bidentata on the other 

 hand does not lay her eggs until the wasp larva has spun its cocoon. 

 No special effort is necessary therefore on the part of neglecta to reach 

 the place where her egg is to be laid ; bidentata, on the contrary, often 

 has to burrow through some earthen stopping, and always to thrust 

 her ovipositor through the wasp's cocoon. Chrysis neglecta is without 

 terminal teeth, bidentata has this armature. 



It would seem then, that in view of these two species at least, the 

 terminal spines are correlated with the necessity of piercing a tough 

 cocoon with the ovipositor. 



This ovipositor is not a sting, but it is very sharp, and I was 

 more than once pricked by it in handling the living insects ; sharp as 

 it is, however, considerable force must be necessary to pierce the 

 cocoon, a portion of the process, doubtless, being widening the opening 

 by pushing the silk aside as the ovipositor progresses, the threads so 

 displaced returning afterwards to their position, as the opening, after 

 the Chrysis retires, is practically closed. In making the opening, the 

 whole work is done by a direct thrust, not by the alternate movements 

 by which the Tenthredo's cut their incisions or the ichneumons of the 

 Bhyssa group penetrate solid wood. In making such a thrust not only is a 

 fulcrum necessary, but even more important is some guidance in order 

 that the thrust may be throughout in exactly the same line and 

 direction. My idea is that the teeth of the margin do not provide a 

 fulcrum, but by pressing down on to the wasp cocoon, make the end 



