Heredity and sex . ts development it must be fertilized. Cellsfrom two individuals must come together to producea new one. The meaning of this process has baffled biologistsever since the changes that take place during fertili-zation were first discovered; in fact, long before theactual processes that take place were in the least un-derstood. There is a rather extensive and antiquatedliterature dealing with the part of the male and ofthe female in the process of procreation. It wouldtake us too far to attempt to deal with these questions THE EVOLUTION OF SEX 5 in their historical aspects, but
Heredity and sex . ts development it must be fertilized. Cellsfrom two individuals must come together to producea new one. The meaning of this process has baffled biologistsever since the changes that take place during fertili-zation were first discovered; in fact, long before theactual processes that take place were in the least un-derstood. There is a rather extensive and antiquatedliterature dealing with the part of the male and ofthe female in the process of procreation. It wouldtake us too far to attempt to deal with these questions THE EVOLUTION OF SEX 5 in their historical aspects, but some of their mostmodern aspects may well arrest our attention. In the simplest cases, as shown by some of the one-celled organisms, two individuals fuse into a singleone (Fig. 1); in other related organisms the two in-dividuals that fuse may be unequal in size. Some-times we speak of these as male and female, butit is questionable whether we should apply to theseunicellular types the same names that we use for the. Fig. 1. — Union of two individuals (Stephanosphcera pluvialis) toform a single individual. (After Doflein.) many-celled forms where the word sex applies to thesoma or body, and not to the germ cells. One of the best known cases of conjugation is thatof paramcecium. Under certain conditions two in-dividuals unite and partially fuse together. An in-terchange of certain bodies, the micronuclei, then takesplace, as shown in Fig. 2, and in diagram. Fig. 3. Thetwo conjugating paramcecia next separate, and eachbegins a new cycle of divisions. Here each individualmay be said to have fertilized the other. The processrecalls what takes place in hermaphroditic animals ofhigher groups in the sense that sperm from one indi-vidual fertilizes eggs of the other. We owe to Maupas the inauguration of an epoch-making series of studies based on phenomena like thisin paramcecium. 6 HEREDITY AND SEX
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Keywords: ., boo, bookcentury1900, bookdecade1910, booksubjectsex, bookyear1913
