OF WASHINGTON. 427 



and consist chiefly in the varying length and direction of the ovi 

 positor and in the mechanism by which this important organ is 

 operated. There is rarely any marked modification in any other 

 organ, though a few exceptions are to be found, such as the 

 strangely altered tarsal joints of the females of the Proctotrypid 

 sub-family Dryininae, fitting these insects for the capture of the 

 active leaf-hoppers, upon which their eggs are placed. 



The larva itself is admirably adapted for its internal and para 

 sitic life, being apodous, soft, colorless, and without specialized 

 structure : but there is little alteration from the form common 

 to the larvae of many aculeate, non-parasitic species. This, 

 at first glance, may seem strange ; but when we remember that, 

 with the exception of the saw-flies, the Hymenopterous larva 

 is a dependent larva, being cared for by the adult in the Arithoph- 

 ila and in the Heterogyna, or hatching in situations where it 

 finds its food already provided, as in the fossorial families 

 and the Cynipidaa, the similarity is accounted for. In short, 

 the typical Hymenopterous larva in the Aculeata is a de 

 pendent creature, well housed and cared for, and these are the steps 

 from which parasitism is easy and which have brought about 

 similar loss of color and structure. 



The mouth-parts show the principal variations, those of the 

 parasitic series being fitted for piercing adipose and connective 

 tissues and absorbing fluids. The mandibles are acute, uniden- 

 tate and falciform. The eyes are represented by simple pigment 

 spots. The antennas are almost lost and the palpi are rudimen 

 tary. The alimentary canal has also become profoundly modified 

 in many of the species, especially in the smaller forms which live 

 gregariously within the host and which are bathed from birth in 

 its blood or softer tissues and absorb their nourishment, especially 

 in early larval life, chiefly by a kind of environmental digestion. 

 Thus we see that in the parasitic Hymenoptera the modifications 

 even of the larva are similar to those which have taken place in 

 the larvae of non-parasitic forms but which live under somewhat 

 similar conditions. On the whole, therefore, modification from 

 the parasitic habit has been less in the insects of this second 

 category than in those of the first ; yet, no doubt, future investiga 

 tion will teach us that more of the characteristics of the adults in 

 the parasitic series, than we now imagine, have resulted from the 

 parasitic habit. 



