208 HYMENOPTEEA. 



blossoms, which act, as applied to this instance of the fertiliza- 

 tion of flowering plants by insects, has been called by Mr. 

 Westwood " caprification." 



Westwood. (Diploleparice Latreille.) Gall-flies. 

 In this most interesting family we have a singular combination 

 of zoological and biological characters. The gall-flies are closely 

 allied to the parasitic Chalcids, but in their habits are plane- 

 parasites, as they live in a gall or tumor formed ~by the ab- 

 normal growth of the vegetable cells, due to the irritation first 

 excited when the egg is laid in the bark, or substance of the leaf, 

 as the case may be. The generation of the summer broods is 

 also anomalous, but the parthenogenesis that occurs in these 

 forms, by which immense numbers of females are produced, is 

 necessary for the work they perform in the economy of nature. 

 When we see a single oak hung with countless galls, the work 

 of a single species, and learn how numerous are its natural 



v. 

 in. 



Fig. 142 



enemies, it becomes evident that the demand for a great nu- 

 merical increase must be met by extraordinary means, like the 

 generation of the summer broods of the Plant-lice. 



The gall-flies are readily recognized by their resemblance to 

 certain Chalcids, but the abdomen is much compressed, and 

 usually very short, while the second, or the second and third seg- 

 ments, are greatly developed, the remaining ones being imbri- 

 cated or covered one by the other, leaving the hind edges 

 exposed. Concealed within these, is the long, partially coiled, 

 very slender ovipositor, which arises near the base of the abdo- 

 men.* Among other distinguishing characters, are the straight 



* Fig. 142. I, abdomen of Cynips quercus-aciculata Osten Saoken, with the ovipos- 

 itor exserted ; II, the same with the ovipositor retracted; III, the abdomen of the 

 female of Fiyitcs (Diplolepis) b-lineatus Say; IV, the same showing the ventral 

 portion, in nature covered by the tergal portion of the abdomen ; V, end view of the 



