94 MAN, THE ANIMAL 



there is a rhythmic ripening and discharge of germ 

 cells which is seasonal for nearly all of the plants 

 and for most animals. Man is the only excep- 

 tion among the higher animals and even here the 

 ova are regularly discharged, thirteen times a year. 

 This is in marked contrast to the constant activity 

 of the salivary glands. 



There comes the age in every child when all of 

 the sex glands become active for the first time. 

 This is known as the period of puberty or adoles- 

 cence, and usually comes on between the ages of 12 

 and 14 years. 



With the onset of puberty, the germ glands, 

 ovaries and spermaries become active. Cells be- 

 gin to grow into mature ova or mature sperms for 

 the first time. This was evident to the earlier 

 students; but what eluded investigation for many 

 years, was the formation of a fluid that is actually 

 secreted by special cells of the ovaries or sper- 

 maries. This secretion is known to-day as the 

 internal secretion of the germ-glands. It is 

 distributed to all parts of the body by the blood 

 and produces changes of far-reaching importance. 

 Common observation of children at this period re- 

 veals their eccentricities, change of voice, growth 

 of hair on the face of the boy; and the much more 

 important change — the change into womanhood 

 and manhood. This last change is the vital one, 



