Aulacini than is shown by this character by other genera of the Cynipini, and this suggests that in this group are the forms most like the ancestral Cynipini.
The galls of this genus are entirely restricted to oaks, the group showing in this respect the extreme specialization of the choice of hosts which is found in all the Cynipini and which is a remarkable condition.
The galls of Neuroterus are, on a whole, comparatively simple but there is some degree of difference in complexity of galls of various species. The differences, however, are not nearly as great as the differences between the galls of two genera of the oak-gall-producing cynipids. The galls of twenty-six species are polythalamous and inseparable, four species have monothalamous galls which are also inseparable, while twenty-two species have monothalamous galls which are separable from the plant. The polythalamous galls (the more primitive type) are always inseparable (a more primitive character); all but a few of the monothalamous (specialized) galls are separable (a specialized character). Some of the species are so primitive as hardly to produce a gall, e. g., Neuroterus virgens and N. calesbæi. Even in the most specialized galls the structure is never highly developed; there is no separation of parts; and there is no production of any abundance of new tissue or peculiar structures. The galls never consist of more than a rather simple wall surrounding the larval cell, rarely with a little simple pubescence, slightly peculiar shape, etc. The larval cell is sometimes quite distinct from the rest of the tissue of the gall, in some species much less so than in others but in no case that I know of is it separable from the rest of the gall. Again, in gall-structure, we find proof of the primitive nature of Neuroterus, more primitive than in any other group of the Cynipini but within the genus showing some considerable evolution. It is likely that further study of the galls may give further warrant for dividing the group into the several genera which have already been proposed for these species.
Reproduction in this group is so closely concerned with alternation of generations that it should be considered in that connection. The life histories of seven species have been studied and in every one of these cases heterogeny has been discovered. It is very likely that in most of the other species of the genus a sirnilar heterogeny exists, but it is extremely important to discover whether all of the species have this sort of life history. The alternate generations, as far as known, always occur on similar parts of the plant, the galls appearing, superficially, rather different, but a closer study shows that in most instances they are of very
