SPECIAL PHYSIOLOGY OF SEX AND REPRODUCTION. 241 



that they can start fresh organisms, and have multiplied to an 

 extent which in most cases makes their liberation a physiological 

 necessity. In the lower animals, the maturity of the sexual 

 functions is often as slightly marked as the liberation of the 

 elements is passive and random. In slightly differentiated 

 organisms, like sponges, there is little reason to suppose that the 

 distinction between cells preponderating in germ-plasma and 

 the ordinary cells of the body is much marked. Nor in such 

 cases is the anarchic opposition between body and reproductive 

 cells at all emphatic, especially as regards the female cells. It 

 is only as the differentiation increases, as the contrast between 

 body-cells and sex-cells becomes emphasised, as the asexual 

 mode of getting rid of surplus wanes, that the typical liberation 

 of sex-elements which marks sexual maturity becomes a striking 

 fact in the life. That the male-cells are always more anarchic, 

 usually mature before the female elements, and even in plants, 

 and in such passive animals as a sponge or a hydra, burst from 

 the organism, while the female cells remain in situ, is quite con- 

 sonant with their predominantly katabolic character. 



§ 2. Sexual Maturation. — I'he maturation of the sexes not 

 only acquires increasing definiteness in the higher forms, but 

 becomes associated with various characteristic accompaniments. 

 The profound reaction of reproductive maturity upon the whole 

 system is best marked in birds and mammals, and perhaps 

 most of all in man. Thus in a young male bird, the circulation 

 in the testes is greatly increased, and these organs increase 

 greatly in size and weight, and commence to develop sperma- 

 tozoa. Meanwhile the "secondary sexual characters" of the 

 adult — gayer plumage for alluring the female, or weapons for 

 contest with other males — make their appearance, the voice and 

 note may alter, and a marked increase of strength and courage 

 may appear. Among mammals, the changes are of similar 

 order, the secondary sexual characters of course differing in 

 detail. The minor changes at puberty in man associated with 

 the commencement of spermatogenesis, are (besides the reflex 

 excitation of erection due to distension of the seminal vesicles, 

 and the more or less periodic expulsion of their contents during 

 sleep) the growth of hair on the pubic region and later on the 

 lower part of the face, and the rapid modification of the 

 laryngeal cartilages and the lengthening of the vocal chords, so 

 rendering the voice harsh and broken during the change, and 

 ultimately deepening it by about an octave. The marked 



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