714 THE PHYSIOLOGY OF REPRODUCTION 



In both sexes the purely physical changes of puberty are 

 accompanied by psychical ones which are no less pronounced. Both 

 kinds of change are dependent largely, if not entirely, upon the 

 functional development of the generative glands.^ 



In animals the general nature of the change which sets in at 

 puberty is similar to that occurring in the human species, and the 

 secondary sexual characters often appear for the first time at this 

 phase of life. Excepting in the case of the domestic animals, little is 

 definitely known concerning the respective ages at which the different 

 species become mature. Most fillies come in use within two years, 

 and all by the time they are three. Cows may come on heat when 

 a year old, but it is best to postpone service until three months later. 

 A good deal depends on nutrition, but even starved and backward 

 cows will receive the bull when fifteen months old. Sows will receive 

 the boar when six months old, and sometimes two months earlier. 

 Sheep will breed at the age of six months (that is to say, lambs 

 born in the spring will breed in the following autumn), but the practice 

 is to be deprecated in the interests both of the ewes themselves and 

 of their lambs. Dogs will breed when about ten months old or even 

 earlier (sometimes seven), but the larger kinds do not breed so soon. 

 Cats are similar. Rodents may breed when still younger, but whether 

 they do so or not depends upon the season of the year and other 

 conditions of environment and nutrition. The white mouse is stated 

 to breed when six weeks old,^ the white rat at about two months,* and 

 the domesticated rabbit at about five months. 



It should be remembered that in animals as in man complete 

 sexuality is not acquired all at once in either sex. Thus, in actual 

 practice, ram lambs are not allowed to serve more than 20 or 25 

 ewes in a season, as against 40 or 50 which older rams may serve. 

 Similarly with stallions, a yearling may serve 15 mares in a season, 

 a two-year old 60, while an adult may serve 80 to 120 mares. 



The Menopause 



In the male sex (as already mentioned) there is no definite age 

 at which the reproductive functions cease. In the female, on the 



size. Runge states further that in one instance he found a corpus luteum in 

 an ovary of a recently born child, but this must be regarded as very exceptional. 

 As a result of his observations, Eunge concludes that follicular maturation seta 

 in during infancy and not at puberty. Ovaries of human embryos showed 

 growing follicles only in very rare instances. 



' For further extensive information see Stanley Hall, AdolesQence, New 

 York, 1904. 



2 Kirkham, " The Life of the White Mouse," Proc. Soc. Exp. Biol, and Med., 

 vol. xvii., 1920. 



^ Donaldson, loc. eit. Evans and Bishop state that the first oestrus occurs 

 between the thirty-seventh and fifty-fifth day ("On the Relations between 

 Fertility and Nutrition," Joii/r. of Metabolic Resea/rch, vol. i., 1922). 



