The buds of _Hydra_ arise as hollow outgrowths from the wall of the column, probably in a definite order and position in each species. The tentacles are formed on the buds much as the buds themselves arise on the column. There is much dispute as to the order in which these structures appear on the bud, and Haacke (Jenaische Zeitschr. Naturwiss. xiv, p. 133, 1880) has proposed to distinguish two species, _H. trembleyi_ and _H. roeselii_, in accordance with the manner in which the phenomenon is manifested. It seems probable, however, that the number of tentacles that are developed in the first instance is due, at any rate to some extent, to circumstances, for in the summer brood of _H. vulgaris_ in Calcutta five usually appear simultaneously, while in the winter brood of the same form four as a rule do so. Sometimes buds remain attached to their parents sufficiently long to develop buds themselves, so that temporary colonies of some complexity arise, but I have not known this to occur in the case of Indian individuals. (c) _Fission._ Reproduction by fission occurs naturally but not habitually in all species of _Hydra_. It may take place either by a horizontal or by a vertical division of the column. In the latter case it may be either equal or unequal. If equal, it usually commences by an elongation in one direction of the circumoral disk, which assumes a narrowly oval form; the tentacles increase in number, and a notch appears at either side of the disk and finally separates the column into two equal halves, each of which is a complete polyp. The division sometimes commences at the base of the column, but this is very rare. Transverse fission can be induced artificially and is said to occur sometimes in natural conditions. It commences by a constriction of the column which finally separates the animal into two parts, the lower of which develops tentacles and a mouth, while the upper part develops a basal disk. Unequal vertical division occurs when the column is divided vertically in such a way that the two resulting polyps are unequal in size. It is apparently not accompanied by any great increase in the number of the tentacles, but probably starts by one of the tentacles becoming forked and finally splitting down the middle.