Nuclear multiplication is usually indirect, the mitosis being, as a rule, more elaborate in the earlier than in the later divisions. The attraction-spheres are generally large and conspicuous, sometimes consisting of a well-developed centrosphere, with or without centrosomic granules, at other times of very large centrosomes with a few astral rays. In those cases where the karyosome is retained, and the sporont-nucleus divides up as a whole, however, the earliest nuclear divisions are direct; the daughter-nuclei being formed either by a process of simple constriction (e.g. _Diplodina_), or by a kind of multiple fission or fragmentation (_Gregarina_ and _Selenidium spp._). Nevertheless, the later divisions, at any rate in _Diplodina_, are indirect. By the time nuclear multiplication is well advanced or completed, the bodies of the two parent-Gregarines (associates) have usually become very irregular in shape, and produced into numerous lobes and processes. While in some forms (e.g. _Monocystis_, _Urospora_, _Stylorhynchus_) the two individuals remain fairly separate and independent of each other, in others (_Lankesteria_) they become intertwined and interlocked, often to a remarkable extent (_Diplodina_). The sexual nuclei next pass to the surface of the processes and segments, where they take up a position of uniform distribution. Around each, a small area of cytoplasm becomes segregated, the whole often projecting as a little bud or hillock from the general surface. These uninuclear protuberances are at length cut off as the sporoblasts or gametes. Frequently a large amount of the general protoplasm of each parent-individual is left over unused, constituting two cystal residua, which may subsequently fuse; in _Diplodina_, however, practically the whole cytoplasm is used up in the formation of the gametes. [Illustration: After Leger, from Lankester's _Treatise on Zoology_. FIG. 13.--Development of the Gametes and Conjugation in _Stylorhynchus longicollis_. a, Undifferentiated gamete, attached to body of parent-individual. b-d, Stages in development of motile male gamete. e, Mature female gamete. f, g, Stages in conjugation and nuclear union of the two elements. h, Zygote (copula). i, Spore, still with single nucleus and undivided sporoplasm.]