Identifier: zologytextbook00cock (find matches)
Title: Zöology; a textbook for colleges and universities
Year: 1920 (1920s)
Authors: Cockerell, Theodore D. A. (Theodore Dru Alison), 1866-1948
Subjects: Zoology
Publisher: Yonkers-on-Hudson, N. Y., World book company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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y red, the other half not. Eachhalf is equally likely to be fertilized by a male- orfemale-producing sperm ; hence there are both red- andwhite-eyed males and females. Similar facts were de-veloped in numerous other cases, proving that the sexchromosome carries other determiners than that forsex, and at the same time confirming the sex chromo-some theory. 7. Although sex is said to be determined by the germ Gynandro-plasm of the zygote, and therefore decided at the mo- ment of fertilization, there are various apparent excep- acters of ... . . • j • •j i both sexes tions and complications. Among insects individuals occasionally appear which combine the characters ofthe two sexes in a remarkable way; these are calledgynandromorphs. A certain kind of parasitic wasp notonly has the sexes differently colored, but whereas themales are winged, the females are wingless. A speci-men was found in which the right side showed the malecharacters, with wings, and the left those of the female,
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Drawing by R. Weber FIG. 19. Face of gynandromorphic bee (Melissodes), the clypeus showing the colorof the male (light) on one side, of the female (dark) on the other. 86 ZOOLOGY Determina-tion ofsexualcharactersthroughsecretions apterous. In a kind of bee (Melissodes) the femaleshave the face black, but in the males a large part of theface (the clypeus) is yellow. A specimen was collectedin Texas, which had the clypeus half yellow and halfblack, the division between the colors perfectly sharpand definite. In other cases the sexual characters arevariously combined, forming a sort of mosaic. Various explanations have been given for thesestrange phenomena, but as Morgan has recently (1914)shown, it is almost certain that they are due to accidentsin cell division at an early stage of growth. If at someearly division, after fertilization, the sex chromosomefails to enter a particular cell, the tissue developing fromthat cell will appear as if the chromosomes in questionhad been absent fro

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