408 



their proportions may be at their first emergence from the egg." 

 With reference to the other orders of insects, he has not been able 

 to get much reliable information ; but he mentions some instances 

 among the Coleoptera, in which the males are thought to be much 

 more numerous than the females ; others in which the females are 

 greatly in excess over the males. As an instance of the latter he 

 quotes a statement made by Mr. Janson to the Entomological 

 Society, " that the females of the bark-feeding Tomicus villosus are 

 so common as to be a plague, whilst the males are so rare as to be 

 hardly known." * In the orders of Hymenoptera and Neuroptera 

 he adduces many instances of the same extreme disproportion, 

 sometimes one sex and sometimes the other predominating. " In 

 some European species of Psocus, thousands of females may be 

 collected without a single male, whilst with other species of the 

 same genus both sexes are common." 



There is one group of Hymenoptera, the gall-making Cynipidce, 

 in which the males of some species " have never been discovered or 

 are excessively rare," and which, from the great ignorance in which 

 we are with regard to many parts of their economy, call for 

 particular investigation. The habits of an American species found 

 on the Black Oak (Quercus tinctoria) are thus described by Mr. 

 Walsh. " The Oak-apples are first observed in May, and reach 

 their full growth in a few weeks ; by the middle of June, male and 

 female gall-flies emerge from a small proportion of them, say one- 

 fourth ; the remaining three-fourths do not develop flies until the 

 autumn, and then produce gall-flies closely allied to, yet quite 

 distinct from those produced in June, and out of thousands of the 

 autumnal flies examined not one was a male." From the result of 

 many experiments in the breeding of these gall-insects, Mr. Walsh 

 was led to infer that " the two forms were not distinct species, but 

 dimorphous forms of the same species." t 



The account of this insect, though a foreigner, deserves notice, 

 from its giving us a clue which may be serviceable in working out 

 the history of some of our own native gall-flies, and it is not at all 

 uulikely that dimorphism will be found to prevail in many other 



* See Ent. Trans, for 1868, Proceed, p. x. 

 t Ent. Trans, for 1869, Prec. p. xii. 



