HEREDITY." 



By L. CuENOT, 

 I'rufcsf<(jr at the I'liivcrnitij of yancy, France. 



The subject Avhich I have with some temerity chosen is far too vast 

 to be treated in a single lecture, so you must not reproach me with 

 being incomplete ; I must voluntarily choose to be so. 



From time immemorial observers have been much impressed by the 

 resemblance which children bear to their parents ; from the latter to 

 the former there is a transmission which is certain, although capri- 

 cious, api^earing to obey no law, and sometimes affecting quite insig- 

 nificant details which are reproduced Avitli striking fidelity. This 

 fact of transmission is known as heredity. 



Before taking up the study of heredity, it is necessary to recall how 

 a new individual, whether of animal or plant, is formed. Let us 

 take, for example, a hen and a cock ; in the interior of the body of the 

 female there is found an organ, the ovary, in which ova are formed, 

 Avhich you know under the name of yolk of ^gg,\ in the male two 

 testicles form little microscopic elements, called spermatozoa. As a 

 result of the sexual union of the two individuals a spermatozoon 

 comes in contact with the ovum and unites with it ; this is the precise 

 act that constitutes fecundation. The fecundated ovum, enveloped 

 with an albuminous coating, the white, Avith a membrane and with a 

 shell is laid or deposited outside the body of the hen and later 

 develops into a little chick. Xow, this chick, when its growth is 

 completed, will present certain characters that are identical with 

 those of the father and others identical with those of the mother; 

 from the one he may derive, for example, a peculiar form of comb; 

 from the other the color of the feathers, etc. It may also be said that 

 in spite of the disproportion of size between the egg and the sper- 

 matozoon neither one of the two parents shows any visible predom- 

 inance in the transmission of characters; there is then in each sexual 

 element, in corresponding equivalent quantity, a substance that con- 



o Trauslation, by permission, of a public lecture given March 17, 1906, at the 

 University of Nancy, under the auspices of the Reunion Biologique, printed in 

 the Revue Scientifique, Paris, April 28, 1900. 



335 



