Sex [electronic resource] . ch asferns and mosses, there are actively locomotorspermatozoa or antherozooids (see Fig. 6), butthough there long seemed to be no inter-mediate step between this and the seeming GS - N-C ^ — 6 Fig. 5.—Ovum and spermatozoon (S) of a sea-urchin, alikemagnified over 750 times, showing relative size. (AfterE. B. Wilson.) The ovum shows the cell-substance orcytoplasm (C) with an intricate structure, the nucleus (N)with readily stainable bodies known as chromatin threads(CHR), and with a nucleolus or germinal spot (GS). static pollen grain of higher plants, a mobilesperm
Sex [electronic resource] . ch asferns and mosses, there are actively locomotorspermatozoa or antherozooids (see Fig. 6), butthough there long seemed to be no inter-mediate step between this and the seeming GS - N-C ^ — 6 Fig. 5.—Ovum and spermatozoon (S) of a sea-urchin, alikemagnified over 750 times, showing relative size. (AfterE. B. Wilson.) The ovum shows the cell-substance orcytoplasm (C) with an intricate structure, the nucleus (N)with readily stainable bodies known as chromatin threads(CHR), and with a nucleolus or germinal spot (GS). static pollen grain of higher plants, a mobilespermatozoon has been found to emerge fromthe pollen tube in certain cycads, and alsoin the strange Gingko or Maiden-hair Treebrought to our gardens from the templeenclosures of old Japan. And the pollen- 36 SEX grains of ordinary flowering plants, althoughthey correspond to the whole male generation,and usually abbreviate away the formationof spermatozoa in adaptation to the loss ofwatery environment, are adapted to passive. Fig. ti.—Female reproductive organ or archegonium in theAdders Tongue Fern—Ophioglossum—and the motilemale cells or antherozooids (SP). The egg-cell is marked0V; it lies in a flask-like recess, the neck of which shows amucous secretion through which the male cells roakotheir way. (After Bruchmann.) transportation, from blossom to blossom, bythe wind or by the agency of insects (Fig. 7). To the question why the dimorphism ofgerm-cells should have been justified in thecourse of evolution, two answers may begiven, (a) A number of facts point to thegeneral conclusion that cross-fertilisation isadvantageous. Darwin first clearly showed— THE EVOLUTION OF SEX 37 and despite some exaggerations his generalconclusion survives—that the progeny ofcross-fertilised plants are more successful and
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