PHYSIOLOGY OF SEX AND REPRODUCTION, 



223 



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 

 consonant with their predominantly katabolic character. 



II. Sexual Maturation.— The maturation of the sexes not only 

 acquires increasing definiteness in the higher forms, but becomes asso- 

 ciated 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 spermatozoa. 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 con- 

 tents 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 strengthening of bones and mus- 

 cles, and the profound psychical changes which accompany the whole 

 series of processes, are also familiar. 



In higher vertebrates, the sexual maturity of the female is marked 

 by a cellular activity within the ovary, not less remarkable than 

 that in the testes. Associated therewith are minor but often very 

 important characteristics, such as the increased mammary development 

 in mammalia. In some of the lower animals, such as certain marine 

 annelids, the ova become so numerous that their disruption or libera- 

 tion is in great part a mechanical necessity. The same might be said 

 of fishes, reptiles, and birds. At the same time the enlargement and 

 escape of the ova are doubtless expressions of a normal cellular 

 rhythm, of which hints are given in the frequent passage from an 

 amoeboid to an encysted phase, in the occasional relapse to the former, 

 and in the fatty degeneration or death of ova which have not accom- 

 plished their destiny. 



The primitive ova of vertebrates lie in clusters in the substance or stroma of 

 the organ, and are produced from the essential germinal epithelium. Only a 

 minority, however, grow into genuine ova ; others, of smaller size, form a 



