PREFACE. THE present volume is devoted to the Nematina, possibly the most difficult group in the entire family ; and, as will be seen, it contains the largest genus, namely, Nematus. The number of species recorded compares very favorably with what is known elsewhere; but I am persuaded that very many species have yet to be discovered in Britain, especially in the North, where they appear to be most numerous Might I therefore express the hope that some of our Entomologists would pay attention to these interesting insects, and thus enable me to describe many additional species in the concluding volume of this work. Especially is it desirable that they be reared from the larvae ; for in Nematus many species are excessively alike in the perfect state, although quite distinct as larvae. Thus, if they be reared from the larvae, not only will our knowledge of their habits be increased, but the specific distinctions will be more clearly defined. I regret that I have not been able to figure more of the larvae, but living as I do in a large city, both the getting and the rearing of the larvae is a work of difficulty.
The phenomenon of Parthenogenesis, now known to be of common occurrence with Sawflies, is a subject well worthy of extended study, and one which, if our knowledge of it were sufficiently comprehensive, might throw light on physiological problems of the highest importance. My third volume will contain the remainder of the Tenthredinidæ, the Siricidæ, and the introductory part of the Cynipidæ, including a discussion on the phenomena relating to the structure and growth of galls in general. The fourth (and concluding) volume will deal with the systematic portion of the Cynipidæ. I have again to thank my correspondents for their kind assistance, and have also to express my indebtedness to the Rev. Prof. T. Wiltshire, M.A., F.L.S., F.G.S., and Mr. R. McLachlan, F.R.S., for having looked over the proofs.MANCHESTER; January, 1885.