The process of gemmation, as seen in _Autolytus_, closely resembles that exhibited by certain Oligochaeta (_Naididae_), where there exists a definite alternation of generations; the production of new individuals by gemmation occurring throughout the greater part of the year, and sexual reproduction recurring only at certain intervals. In the Polychaeta such alternation exists in _Myrianida_; but it is only the terminal link of a series, which takes its starting-point in the process exhibited by the majority of Annelids, where no sexual character marks maturity. The next stage is presented by "epigamous" forms like Heteronereis and Heterosyllis; then "schizogamy" makes its appearance in certain Syllidae, resulting in the formation of two morphologically and physiologically distinct individuals which lead independent lives. The appearance of a head and of a zone of proliferation leading to the formation of a chain of sexual zooids is accompanied by a delay in the appearance of the genital organs, for in _Autolytus_ these arise _during_ the formation of the new individuals, as part of the general process of new formation; whilst in _Myrianida_ the delay is prolonged, and the generative elements do not make their appearance till _after_ the new individuals have reached some size. More simple cases of the separation of the body into two parts, sexual and asexual, occur also in some of the Serpulidae. Thus in _Filigrana_ and _Salmacina_ the generative elements make their appearance in the hinder segments, as they do throughout the Sabelliformia; and this hinder part of the body separates {282}from the anterior region after the formation of a new head between the two regions.[336] Another modification of the process of budding and fission is exhibited by _Syllis ramosa_, one of the most interesting forms of animal life which was obtained by the "Challenger." This worm consists of a main stem, whence arise a number of lateral branches, which may also branch so as to give rise to an arborescent colony (Fig. 150). The branches of the first and second and higher orders arise by budding from the sides of the original form or branches of lower order; and some of these branches develop generative products, and bud forth a head near the point of attachment. These sexual branches, no doubt, separate from the colony and distribute the ova. The worm lives in a Hexactinellid sponge, _Crateromorpha meyeri_, living in depths of 95 to 140 fathoms in the Eastern seas.[337] [Illustration: FIG. 150.—Portion of _Syllis ramosa_. (Reduced from M‘Intosh.)]