. The cell; outlines of general anatomy and physiology. n intermittent and stag-gering movement. After ashort time the fusion is so faradvanced that the two gametesform a single thick oval body,which, however, betrays itsderivation from two indi-viduals by containing two pig-ment spots and four flagella(e,/). The zygote now gradu-ally slackens its movements,until finally it comes to rest;it then loses its four flagella,which are either drawn in or thrown off, becomes globular in shape, and surrounds itself witha cell-wall. Frequently the resting stage begins only a few minutes afterthe commenc
. The cell; outlines of general anatomy and physiology. n intermittent and stag-gering movement. After ashort time the fusion is so faradvanced that the two gametesform a single thick oval body,which, however, betrays itsderivation from two indi-viduals by containing two pig-ment spots and four flagella(e,/). The zygote now gradu-ally slackens its movements,until finally it comes to rest;it then loses its four flagella,which are either drawn in or thrown off, becomes globular in shape, and surrounds itself witha cell-wall. Frequently the resting stage begins only a few minutes afterthe commencement of pairing ; in other cases, however, the zygotemay swim round in the water with its four flagella for threehours, in a naked condition, without a membrane, until finally itdraws in its flagella, and sinks to the ground. The gradual appearance of sexual differentiation can befollowed still better in the very numerous species of lower Algae,in which the fertilisation of gametes occurs. As in Spirogyra (Fig. 153), one of the two individuals, which. Fig. 155.—Botrydium granulatam (afterStrasburgtr, Fig. 139) : A free plant ofmedium size (x28); J5 swarm-spore, fixedwith iodine solution (x510); C a single individual; b two isogameteswhich have just come into contact; c, d,and e the same lying side by side; / zygote,produced by the complete fusion of thegametes (x510). 286 THE CELL in other respects are absolutely similar, may be called female,since it remains at rest, and must be sought for by the other forthe purposes of conjugation. Thus a relationship, similar to thatseen in Ph&eosporese and Cutleriaceas, is produced. In some species of Phseosporese, the male and £emale swarm-spores cannot be distinguished from one another when they areevacuated from the mother-cell; they are of the same size, andare each provided with a pigment spot and two flagella ; theydo not pair whilst they are swimming about. However, adifference between the gametes soon becomes appar
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