. The cell; outlines of general anatomy and physiology. oundation of anew series of generations. Such cycles are termed generationcycles. They occur in the whole organic kingdom in the mostvarious forms. In unicellular organisms, for instance, the generation cycleconsists of a large number of independent individuals, whichsometimes amount to thousands. The fertilised elementaryorganism multiplies by repeated divisions, producing descendants,which do not require fertilisation, until a period arrives when anew generative act occurs between the generations which have beenproduced asexually. These
. The cell; outlines of general anatomy and physiology. oundation of anew series of generations. Such cycles are termed generationcycles. They occur in the whole organic kingdom in the mostvarious forms. In unicellular organisms, for instance, the generation cycleconsists of a large number of independent individuals, whichsometimes amount to thousands. The fertilised elementaryorganism multiplies by repeated divisions, producing descendants,which do not require fertilisation, until a period arrives when anew generative act occurs between the generations which have beenproduced asexually. These phenomena have been most carefullyobserved in Infusoria. Thus Man pas (VII. 30, p. 407) has proved 252 THE VITAL PROPERTIES OF THE CELL. 253 by a number of experiments upon Leucophrys patala, a species ofInfusorian, that only after 300 generations have been producedfrom a fertilised individual does the generation cycle close, thedescendants now showing for the first time the inclination andcapacity for sexual conjugation. In Onychodromus grandis this. Fig. 137.—Development of Pandorina morum (after Pringsheitn ; from Sachs, Fig. 411):I a swarming colony ; II the same, split up into sixteen daughter-colonies; III asexual family, through the gelatinous envelope of which the individual cells are passingout; IV, V conjugation of the swarm-spores; VI a newly-formed zygote; VII a full-grown zygote ; VIII transformation of the contents of a zygote into a large swarm -Cell; IX the same, after having been set free; X the young colony derived from theswarm-cell. condition occurs after the 140th generation, and in Siylouichia2>iistn1ata, after the 130th generation. In multicellular organisms the cells, which are produced by the 254 THE CELL division of a fertilised egg, remain associated together, forming acolony of cells or an organic individual of a higher order. Re-garded from the common point of view, from which we here treatthe sexual question, they may be compared to the colle
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