REPRODUCTION. 55 



ganization is complete at its birth, would suffice for the evolution of many 

 millions of frogs. Besides, the parent having once evacuated the pro- 

 duct of her fecundation, has done with it : the tadpoles issuing from the 

 ova find their nourishment in the outer world -, but the young mammal 

 derives its sustenance from the mammae of the mother, at whose expense 

 it continues, for a more or less protracted period, to live as a parasite. 

 With the higher animals, which give birth to an incomplete being, there 

 is observed an increase in fecundity : the Bitch only yields two per cent, 

 of its weight, but the Calf absorbs twenty per cent, of its parent's weight. 

 This unequal distribution of fecundity among the animal species is a 

 conservative element in the scheme of organic nature. The reproduc- 

 tiveness and the numerous chances of destruction surrounding the germs, 

 are compensated for in just proportion ; for out of many thousand ova 

 furnished by the most prolific species, a comparatively limited number 

 only find all the conditions favorable for their development. 



chaptp:r I. 



The acts by which generation is accomplished are four : these are 

 copulation., feamdation^ gestation., Vixvdi parturition ; but it is only on the at- 

 tainment of a certain age — that of puberty — that these sexual offices are 

 in activity, and they continue so for a variable period, according to the 

 species. During this time, ova from the ovaries, fecundated by the male 

 seminal fluid, are received into the uterus, and remain there for a reg- 

 ulated period, until they have become transformed into young creatures 

 possessing certain physical attributes and resemblances to their parents. 

 This is the gestation period, and is followed by that of parturition, when 

 the young are born. 



SECTION I. PUBERTY. 



The generative organs of the domesticated female animals are, like 

 those of the human female, only in a state of activity during the prime of 

 life ; and the most notable characteristic of their functions, as in woman, 

 is their periodicity. These functions commence at puberty, when cer- 

 tain very marked modifications occur throughout the whole organism, but 

 particularly in the generative organs of the male and female animals. 

 In the first the testicles become more voluminous, and in some 

 species they leave the abdominal cavity to be lodged in the scrotum ; 

 they also begin to secrete an abundance of a special fluid — the " sper- 

 matic," in which particles of a definite shape — spermatozoa — endowed 

 with motion, appear. This fluid is stored up in the vesiculce seminales 

 which, until this period, were small and wasted-looking. The organ for 

 the conveyance of this spermatic fluid to the female becomes more 

 developed, and is capable of complete and frequent erection. In the 

 female the mammae enlarge, the ovaries are more vascular and turgid- 

 looking than before, and the Graafian vesicles are more or less devel- 

 oped. The periodic ovipont then begins to be carried on, with all the 

 distinctive peculiarities which it is to bear during the prolific period of life. 



The age at which animals ^xnvQ 3.tpuberty or sexual maturity, is not 

 only different in different species, but is influenced to some extent by the 

 rapidity of their growth and the duration of their life. Domestication has 



