ItKI'Unin'CTinX. 65 



BOOK II. 



OBSTETRICAL PHYSIOLOGY. 



REPRODUCTION. 



Having described the situation, structure, and peculiarities of the 

 external and internal orfj;ans of the female domesticated animals, we 

 have now to inquire into their functions. Some of these functions have 

 for their end the conception, development, and preservation of the young 

 animal for a certain period, until it can maintain a more or less inde- 

 pendent existence, when others of them are brought into play in order 

 to place it in direct relation with the external world in the act of 

 parturition, while others cease. But in order that generation should 

 take place in the higher classes of animals, it is necessary that the two 

 sexes be placed in favourable relations with each other. This pre- 

 liminary condition is indispensable, as the essential of reproduction is 

 the contact with, and action of the male fecundating fluid on, the ovum 

 of the female. Nature has ordained that this creative act should be 

 accomplished by engendering in these animals an instinctive, copulative, 

 and irresistible desire at a certain stage of existence ; which desire, 

 continuing only for a brief period, is renewed after particular intervals, 

 until the faculty of reproduction ultimately ceases. 



The advent of the power of reproduction in the male and female sex 

 of animals is very unequal among the various species, and is generally 

 in relation to the duration of their existence — the creatures which are 

 short-lived being capable of bringing forth young at an earlier period of 

 life than those which enjoy a longer term. 



The Elephant only brings forth one at birth, and this occurs but once 

 in three or four years ; while the descendants of the Kabbit in tlie same 

 space of time may be reckoned at more than a million. This great 

 disparity has nothing of chance or accident in it, but is in admirable 

 harmony witli the designs of Nature. The individuals of every species 

 produce, as has been justly remarked by Verheyen, a total number of 

 germs which amply covers the losses caused by death ; and the prema- 

 ture destruction of many of these germs is likewise a providential safe- 

 guard against their too numerous multiplication. 



Two factors regulate fecundity ; these comprise the nutritive excess 

 which the maintenance of the individual renders disposable, and the 

 sum total of the materials necessary for the embryonic evolution ; but 

 tlie divergences of these two factors are as extensive as those of fecun- 

 dity itself. 



If we take the weight of the foetus at birth as the equivalent to the 

 nutritive matter that the parent has endowed it with, and multi])ly this 

 weight by the number of young annually produced, we shall obtain the 

 total amount of the materials which have been derived from the 

 maternal organism. Theti weighing the mother, and comparing her 

 weight with that of the foetus, we shall arrive at tlie disposable nutritive 

 excess; and from this, according to Leuckart, be able to calculate the 

 fertility of a species. Although this calculation is only approximate, it 

 none the less demonstrates, in principle, the relations between fecundity 

 and the two before-mentioned factors. This is shown in the following 

 table, drawn up by Leuckart, with reference to the domesticated 

 animals. 



