An allied genus, _Polynema_, has also very curious larvæ. The perfect insect is aquatic in its habits, swimming by means of its wings; flying, if we may say so, under water.[15] It lays its eggs inside those of Dragon-flies; and the embryo, as shown in Fig. 28, has the form of a bottle-shaped mass of undifferentiated embryonal cells, covered by a thin cuticle, but without any trace of further organization. Protected by the egg-shell of the Dragon-fly, and bathed in the nourishing fluid of the Dragon-fly’s egg, the young _Polynema_ imbibes nourishment through its whole surface, and increases rapidly in size. The digestive canal gradually makes its appearance; the cellular mass forms a new skin beneath the original cuticle, distinctly divided into segments, and provided with certain appendages. After a while the old cuticle is thrown off, and the larva gradually assumes the form shown in Fig. 29. The subsequent metamorphoses of _Polynema_ offer no special peculiarities. [Illustration: FIG. 28, Embryo of _Polynema_ (after Ganin). 29, Larva of _Polynema_—_asch_, rudiments of the antenna; _flsch_, rudiments of the wings; _bsch_, rudiments of the legs; _vfg_. lateral projections; _gsch_, rudiments of the ovipositor; _fk_, fatty tissue.] From these facts—and, if necessary, many more of the same nature might have been brought forward—it seems to me evident that while the form of any given larva depends to a certain extent on the group of insects to which it belongs, it is also greatly influenced by the external conditions to which it is subjected; that it is a function of the life which the larva leads and of the group to which it belongs.