. The cell; outlines of general anatomy and physiology. and female, that is to say, both impart-ing and receiving. Fixed forms of Infusoria, however, such asVorticellce, etc., behave in an interesting and somewhat differentfashion. The Epistylis umbellavia(Fig. 149) may serve as anexample. When a conjuga-tion period is approaching,several individuals of thecolony of Vorticellae dividerapidly and repeatedly, thusproducing a generation ofindividuals (r) very inferiorin size to the mother organ-ism. Other individuals ofthe colony remain undividedand of normal size. Theformer are called microga-me
. The cell; outlines of general anatomy and physiology. and female, that is to say, both impart-ing and receiving. Fixed forms of Infusoria, however, such asVorticellce, etc., behave in an interesting and somewhat differentfashion. The Epistylis umbellavia(Fig. 149) may serve as anexample. When a conjuga-tion period is approaching,several individuals of thecolony of Vorticellae dividerapidly and repeatedly, thusproducing a generation ofindividuals (r) very inferiorin size to the mother organ-ism. Other individuals ofthe colony remain undividedand of normal size. Theformer are called microga-metes, and the latter macro-gametes ; they differ fromone another sexually. Each microgamete detaches itself from its stalk, swims roundin the water, and after a short time attaches itself to a macro-gamete in order to conjugate with it (Fig. 149 k). Changesoccur in the nuclear apparatus similar to those described in detailabove in the Param&scium, and migratory nuclei are exchanged herealso. However, the macrogamete alone continues to develop, the. Fig. 149.—Epistylis umbellaria fafter Graeff;from R. Hertwig, Fig. 142) : portion of a colonyin the act of conjugation ; r microzoids pro-duced by division ; k microgametes in conjuga-tion with macrogamete8. 272 THE CELL migratory and stationary nuclei of the primary division spindlecoalescing, whilst the corresponding structures in the microgameteare, as it were, paralysed, and, instead of fusing and developingfurther, degenerate and become dissolved, like the fragments ofthe chief nucleus and the subsidiary spindles. In this manner the microgamete loses its independence andindividuality, and becomes gradually absorbed into the macro-gamete, increasing the size of the latter. Thus, in consequence of the stationary mode of life of Vorticella,a peculiar sexual dimorphism has developed, resulting in the ab-sorption of the smaller of the conjugating individuals, after it hasfunctioned to a certain extent as a male element in fertilisin
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