24-36 The Zoologist — January, 1871. 



are evidently parasitic, make this supposition scarcely probable. 

 Further researches are necessary." 



The supposition wliich Dr. GiraucI thought scarcely probable, 

 that the Isosonia is wholly herbivorous, has been ascertained in 

 America to be a fact. One more, and as yet unpublished, discovery 

 has been made as to the economy of Isosonia. Mr. MoncreafF has 

 reared Isosoma hyalipennis and Bracon tenuicornis from galls on 

 Triticum repens. He also reared Decatoma mellea, Pteromalus 

 fulviventris and P. Festuca) (n. sp.) from galls on Festuca. 



It appears then that Pimpla graminella) (an ichneumon fly 

 abundant in England) is a noxious rather than a beneficial insect; 

 for even if, as Dr. Giraud thought, it is carnivorous and feeds on 

 Ochthiphila in early life, it soon becomes herbivorous and is more 

 injurious to the jilants than the little two-winged fly which it 

 succeeds. There is need of much inquiry to ascertain whether 

 many species of Ichneumonida) resemble it in this particular. 



As Isosonia feeds chiefly on grasses, it is probabl}' an inhabitant 

 of most parts of the globe. Three species have been discovered 

 by Mr. Darwin in Australia. In America Isosoma diminishes mucli 

 the materials for bread and wine, but Mr. Rile}', as appears by the 

 following extract, is of opinion that such is not likely to be the 

 case in Europe : — " Since, then, it can be demonstrated by hard, 

 dry facts, that American plants and insects do not become natu- 

 ralized in the Old World with anything like the facility with which 

 the plants and insects of the Old World are every day being 

 naturalized in America, there must be some cause or other for this 

 singular state of things. What is that cause ? It is, as we believe, 

 a simple fact which is pretty generally recognized now as true by 

 modern naturalists, namely, that the plants and animals of America 

 belong, as a general rule, to an old-fashioned creation, not so highly 

 improved and developed as the more modernized creation which 

 exists in Europe. In other words, although this is popularly known 

 as the New World, it is in reality a much older world than that 

 which we are accustomed to call the Old World. Consequently, 

 our plants and animals cannot stand their ground against European 

 competitors imported from abroad. There is another reason why 

 the insects which are imported into this country multiply at a 

 prodigious rate, and soon acquire herculean power of doing harm, 

 though they may never have stepped beyond the limits of propriety 

 in their own native home — a reason too palpable and evident to 



