. The biology of the Protozoa. Protozoa; Protozoa. 530 BIOLOGY OF THE PROTOZOA ib) Gametic Meiosis (Wilson, 1925).-In the preceding section instances of meiotic divisions subsequent to cell fusion were inter- preted as due to stimuli mutually imparted to the conjugating individuals. For this the protoplasm must be in a mature condition, that is, with an organization conside^abl^' modified from^ that of the young or immature organisms. In a later section evidence is given which indicates that under proper conditions the stage is all set for a similar all or none series of phenomena without howe
. The biology of the Protozoa. Protozoa; Protozoa. 530 BIOLOGY OF THE PROTOZOA ib) Gametic Meiosis (Wilson, 1925).-In the preceding section instances of meiotic divisions subsequent to cell fusion were inter- preted as due to stimuli mutually imparted to the conjugating individuals. For this the protoplasm must be in a mature condition, that is, with an organization conside^abl^' modified from^ that of the young or immature organisms. In a later section evidence is given which indicates that under proper conditions the stage is all set for a similar all or none series of phenomena without however, the stimulus of contact (see p. 540, endomixis). The latter con- dition termed here gametic meiosis if accompanied by the cell fusion of gametes, is characteristic of the majority of Protozoa. Fig. 221.—Actinosphcerium eichhornii. A, two gametes ("cystospores No. 2") resulting from the division of the same mother-oell; B, both "polar bodies" are formed in the right gamete, the second one forming in the left gamete; C, the cell bodies of the gametes have fused, and the nuclei are fusing; D, young organism leav- ing cyst; p, p^ P^ "polar ; (After Hertwig.) in which fertilization is accomplished hy the fusion of cells. Unfor- tunately the history of the chromosomes is known in but few cases but there is scarcely a paper on the fertilization of Protozoa that does not describe two rapidly-following divisions of the nuclei prior to fusion, and these are called maturation divisions, and the resulting nuclei "reduction ; In Actinosphcprivm eichhornii according to Hertwig (1S9S) the first evidence of the process is encystment of the adult organism and excretion of waste matters contained in the protoplasm. The nuclei are reduced in number to from 5 to 10 per cent of the original number by fusion and absorption in the protoplasm. The cell then divides into as many daughter cysts as there are nuclei and these Hertwig calls cytos
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