74 



A. A. Grirault: 



is distinctly longer, as long or nearly as the submarginal, thrice or 

 more the length of the stigmal, while in Uscana it is only half the 

 length of the submarginal and twice the legth of the stigmal. Also in 

 Uscana the ovipositor is short, inserted at base of distal half of abdomen, 

 not exserted and the abdomen is short, not long and conic-ovate, 

 the ovipositor long and prominent, its valves distinctly though shortly 

 exserted as in Pterygogramma; also the discal ciliation of the fore 

 wing is more dense. 



5. The Characteristics of the Trichogrammatidae. 



A student of those parasitic Hymenoptera grouped together under 

 the name of chalcid flies soon learns to pick out the various groups, 

 by the eye or more definitly by their habitus. Members of the natural 

 f amilies usually have distinct peculiarities of ensemble; an encyrtid 

 looks an encyrtid, an eulophid an eulophid, a pteromalid a pteromalid 

 and so on. Each gives a distinct impression. So a mymarid looks a 

 mymarid and a trichogrammatid a trichogrammatid — in many. cases. 

 All members of this family of egg-parasites have a more or less characte- 

 ristic appearance to the naked eye and a specialist soon gets to know 

 this. Nevertheless, while one can recognise a chalcidid for instance 

 with certainty without a great number of exceptions, in the case of tricho- 

 grammatids a larger number of exceptions occur and in a number 

 of cases it will be impossible to say whether the insect is an encyrtid, 

 an eulophid or a trichogrammatid without more careful examination 

 of it. Thus, while there are always a certain number of individuals 

 of all the f amilies which do not partake of the ensemble of their par- 

 ticular family, with the Trichogrammatidae the number of individuals 

 of this kind appears to be larger and most members of the family 

 give an aphelinine or encyrtine impression. Koughly, our gross sense 

 impressions serve the purposes of taxonomy since in most cases they 

 reflect the resemblences which the members of a segregate usually 

 possess; these resemblences throughout all organic nature usually 

 meaning common descent and close relationship. A large group of 

 closely allied species will give a gross impression of likeness, though 

 when examined under the microscope they will be seen to differ greatly 

 in their details falling into a number of natural genera many of which 

 will be unlike in many important structures. Still the gross impression 

 sums up, as it were, the true relations of the whole group, the lesser 

 units affording many exceptions. Thus one may see an eulophid 

 resembling so closely a Gonatocerus that it is impossible to detect 

 which is which until closer scrutiny reveals the real differences. 

 Hence, one will be often Struck when collecting trichogrammatids 

 with encyrtine and aphelinine impressions and it is impossible to 

 prevent the idea arising that these gross impressions hint at a hidden 

 relationship between the three. Scrutiny confirms this. Members of 

 the family bear both encyrtine and apheline characters but the latter 

 predominate and according to those principles enunciated above we 



