THE DEVELOPMENT OP THE EMBRYO ITSELF. 119 



opment ; and in vertebrates one of the most pronounced epochs 

 —in fact, the most marked of all — is that by which the young 

 organism, through a series of rapid stages, attains to sexual ma- 

 turity. 



While the growth and development of the generative organs 

 share to the greatest degree in this progress, other parts of the 

 body and the entire being participate. 



So great is the change that it is common to indicate, in the 

 case of the human subject, the developed organism by a new 

 name — the " boy " becomes the " man," the " girl " the " woman." 

 Relatively this is by far the most rapid and general of all the 

 transformations the organism undergoes during its extra-uter- 

 ine life. In this the entire body takes part, but very unequally. 

 The increase in stature is not proportionate to the increase in 

 weight, and the latter is not so great as the change in form. 

 The modifications of the organism are localized and yet affect 

 the whole being. The outlines become more rounded ; the pel- 

 vis in females alters in shape ; not only do the generative organs 

 themselves rapidly undergo increased development, but certain 

 related glands (mammse) participate ; hair appears in certain 

 regions of the body ; the larynx, especially in the male, under- 

 goes enlargement and changes in the relative size of parts, re- 

 sulting in an alteration of voice (breaking of the voice), etc. — 

 all in conformity with that excess of nutritive energy which 

 marks this biological epoch. 



Correlated with these physical changes are others belonging 

 to the intellectual and moral (psychic) nature equally impor- 

 tant, and, accordingly, the future being depends largely on the 

 full and unwarped developments of these few years. 



Sexual maturity, or the capacity to furnish ripe sexual ele- 

 ments (cells), is from the biological standpoint the most impor- 

 tant result of the onset of that period termed, as regards the 

 human species, puberty. 



The age at which this epoch is reached varies with race, 

 sex, climate, and the moral influences which envelop the indi- 

 vidual. In temperate regions and with European races puberty 

 is reached at from about the thirteenth to the eighteenth year 

 in the female, and rather later in the male, in whom develop- 

 ment generally is somewhat slower. Changes analogous to the 

 above occur in all vertebrates. It is at this period that differ- 

 ences of form, voice, disposition, and other physical and psychic 

 characteristics first become pronounced. 



