Thus the ordinary type of Hymenopterous larva, as we have already seen, is a fleshy apod grub; although those of the leaf-eating and wood-boring groups, Tenthredinidæ and Siricidæ (Fig. 14), are caterpillars, more or less closely resembling those of Lepidoptera. There is, however, a group of minute Hymenoptera, the larvæ of which reside within the eggs or larvæ of other insects. It is difficult to understand why these larvæ should differ from those of Ichneumons, which are also parasitic Hymenoptera, and should be, as will be seen by the accompanying figures, of such remarkable and grotesque forms. The first known of these curious larvæ was observed by De Filippi,[13] who, having collected some of the transparent eggs of a small Beetle (_Rhynchites betuleti_), to his great surprise found more than half of them attacked by a parasite, which proved to be the larva of a minute Hymenopterous insect belonging to the Pteromalidæ. Fig. 15 shows the egg of the Beetle, with the parasitic larva, which is represented on a larger scale in Fig. 16. [Illustration: FIG. 14, Larva of _Sirex_ (Westwood, loc. cit.). 15, Egg of _Rhynchites_, showing the parasitic Larva in the interior. 16, the parasitic Larva more magnified.] More recently this group has been studied by M. Ganin,[14] who thus describes the development of _Platygaster_. The egg, as in allied Hymenopterous families, for instance in _Cynips_, is elongated and club-shaped (Fig. 17). After a while a large nucleated cell appears in the centre (Fig. 18). This nucleated cell divides (Fig. 19) and subdivides. The outermost cells continue the same process, thus forming an outer investing layer. The central, on the contrary, enlarges considerably, and develops within itself a number of daughter cells (Figs. 20 and 21), which gradually form a mulberry-like mass, thus giving rise to the embryo (Fig. 22). [Illustration: FIG. 17, Egg of _Platygaster_ (after Ganin). 18, Egg of _Platygaster_ showing the central cell. 19, Egg of _Platygaster_ after the division of the central wall. 20, Egg of Platygaster more advanced. 21, Egg of _Platygaster_ more advanced. 22, Egg of Platygaster showing the rudiment of the embryo.]