The life histories of the Selaginellas evidence some important differences which call for special comment. Here throughout the whole family the spore-bearing part of the plant is in the form of very definite cones. As in the case of Lycopodium there is only one sporangium to each leaf, but they are of two kinds. One, on account of the fact that it is responsible for the production of small spores, is called the microsporangium; the other, the megasporangium. The two kinds of sporangia are usually present on the same cone, although the microsporangia are as a rule higher up the stem than the megasporangia. The number of microspores produced is very large, but only four megaspores are borne in each megasporangium. The megaspores are, of course, very much larger than the microspores. The germination of the megaspores is started in the sporangium; at a certain point in their development they are shed. In the case of the microspores germination commences after the spores have fallen on to moist soil. The prothallus is exceedingly small, being little more than a group of cells forming an antheridium. Should there be sufficient moisture about, the spermatozoids which are produced by the antheridium swim towards the archegonia in any female prothallus which may be near. Fertilization then takes place, and the final outcome is the young plant. Now and again in certain species it is seen that the megaspores develop to such an extent within the sporangium that fertilization takes place, and even an embryo or young plant may be formed.