List uf the Insect Fauna of the County. 117 



flies, should certainly be carefully studied. The agaruous 

 genera Aphiluthrix, Neurote^nis, Dryophaiita, and Biorhiza are 

 but aBstival parthenogenetic generations of the sexual genera 

 Ancb'ictis, Simthegaster , and Triyonaspis, but Dr. Adler still 

 leaves four species of Aphilothrix [A. seminationis, Gir., A, 

 margiyialis, Sclilecht., A. quadrilineatus, Hart., and A. alho- 

 punctata^ Sclilecht.) whose generations, he tells us, are ex- 

 clusively parthenogenetic — " the alternate sexual generation 

 does not exist." Cyyiips is still untouched. This varying 

 biography and linking of structurally different forms into one 

 species is deeply interesting, and leads to most important 

 considerations and results which we cannot now further 

 follow out. 



Amongst the cynipideous gall-makers the genus Bhodites 

 limits itself to the rose, and other species produce galls on 

 the bramble, ground-ivy, Hieracium, Potentilla, poppy, &c. 



The larvae of the Cynipidse are fat, fleshy, apodal, whitish 

 grubs ; they pupate in the galls, without exception. 



"We have but few British sawflies which produce galls, and 

 I am only able to include three species in our Essex list. 

 These all occur on willows, and are produced by species of 

 the Nematidse. The very common bean-shaped gall of 

 Nematus gallicola, which is so commonly seen projecting from 

 both sides of the leaf of many willows, must be well known 

 to all. Its manner of reproduction is very commonly 

 parthenogenetic, the male N. gallicola being excessively rare. 

 The late Mr. F. Smith did not meet with it until 1873, the 

 year before his death ; and he worked assiduously at the 

 Hymenoptera for upwards of fifty years. It is somewhat 

 remarkable that a beetle [Balaninus BrassiccB) is a very general 

 inquiline, or lodger, in these galls. Unlike the Cynipidae, the 

 gall-making sawflies do not undergo their metamorphoses 

 within the gall, but the larvae leave it when full-fed and pupate 

 in the ground. The Cryptocampi are an exception ; their 

 cocoons are formed within the woody galls. 



In the Diptera, as in the Hymenoptera, we have one large 

 gall-producing family — the Cecidomyids, whose numerous 

 species are commonly known as gall-gnats. Seventy-six 



