File:Sex (electronic resource) (1914) (14774172051).jpg

Identifier: b20442221 (find matches)
Title: Sex (electronic resource)
Year: 1914 (1910s)
Authors: Geddes, Patrick, Sir, 1854-1932.
Subjects: Sex
Publisher: New York : H. Holt and company London : Williams and Norgate
Contributing Library: Wellcome Library
Digitizing Sponsor: Wellcome Library

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starfish from a female, or a female froma male sea-urchin. Nor can we see that theone sex is attracted to the other. Thefertilisation of the eggs is more or less hap-hazard, but it must be noted that large num-bers of individuals are found living together,and that the males and females becomemature about the same time. Both ova andspermatozoa are set adrift in the sea, and asthere are thousands of sperms for every ovumthe chance of fertilisation is much greaterthan wrould at first sight appear likely.Moreover, from within a short distance thereis a chemotactic M attraction of the sperma-tozoa to the ova (see Fig. 9). It should be noted that animals like sea 48 SEX urchins with superficially similar sexes atfenone the less in a sense very sexual, at thebreeding season at least, for they produceenormous quantities of eggs and sperms, andthe reproductive organs are huge in proportionto the body. Thus one of the British star-fishes (Luidia ciliaris) produces at least 200millions of eggs.
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Figi. 9.—Fertilisation of ovum of starfish—after Fol. InI the spermatozoa are seen surrounding the ovum,which is enveloped in a delicate zone of mucus. Aminute receptive cone is seen on the surface of theovum. In II a spermatozoon is entering, the locomotortail is seen protruding, a membrane is being rapidly formedaround the ovum. In III the spermatozoon has entered,the membrane is completed, the ovum has become non-receptive. Only a small part of the ovum is shown; As we ascend the series, the evolution ofsex-dimorphism becomes gradually apparent.Following the differentiation of tissues andstructures accessory to the reproductive organsthe body itself begins as a whole to be sexed.Various structures, quite extra-genital, beginto have alternative expressions, more or lessmutually exclusive, and masculine and femi-nine individuals thus at length appear.Animals began to put on secondary sex THE EVOLUTION OF SEX 49 characters; and this was the great step ofsex-dimorphism. It need har

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