148 Heredity. 



SECTION I. DIRECT HEREDITY. 



I. 



We have first to resort to physiology in order to clear the field, 

 since the laws of physiological heredity have been oftener and far 

 better studied than those of moral heredity ; yet so close is the 

 connection between the two orders of facts, that a person can 

 hardly study the one without the other. 



In the case of direct heredity, the concurrence of the two sexes 

 in the formation of the product is now admitted by all physiolo- 

 gists. We need, therefore, only refer to the ancient doctrines of 

 the spermatists and the ovists. The former held that, notwith- 

 standing the apparent concurrence of both sexes in generation, 

 the germ is contained in the male element alone. The latter, who 

 held a doctrine the very reverse of this, but equally exclusive, 

 maintained that the germ exists only in the female element. The 

 first doctrine, which was adopted by Galen, Hartsoeker, Boerhaave, 

 Leeuwenhoek, and the second, which was held by Malpighi, 

 Vallisnieri, Spallanzani, Bonnet, Haller, and even De Blainville, 

 are now equally abandoned. It is admitted that the child is 

 sprung from both father and mother, and embryology demon- 

 strates this. But opinions diverge in regard to the part taken 

 by each of the parents. 



If we take a purely theoretic point of view, it is easy enough to 

 formulate the law of direct heredity. According to P. Lucas, it 

 would consist in the 'absolute equilibrium in the physical and 

 moral nature of the infant of the integral resemblances of the 

 two parents.' The procreated individual would be, everywhere and 

 always, nothing but the exact mean of his two parents ; the dis- 

 tinct characters of both would be reproduced in their progeny 

 in every portion of his body, and in every faculty of his mind. 

 But this is only a logical hypothesis, which very rarely becomes a 

 reality in the higher animals ; and it is hardly rash to say that the 

 law has never been met with in this ideal form. 



And yet we understand that this is the law, that is to say, the 

 only formula broad enough to include all the phenomena; the 

 only rule which flows of necessity from the nature of things, and 

 which expresses the essence of heredity. 



