398 Beard, Heredity and the epicycle of the germ-cells. 



Heredity and the epicycle of the germ-cells 

 by J. Beard, D. Sc., 



University Lecturer in Comparative Embryology, Edinburgh. 



(Schluss.) 



It is it, and it alone, which permits of the Landing 1 down of the 

 characters of one generation to future generations. It is the veiy 

 basis of heredity. The formation of like primary germ- cells and their 

 essential similarity or equivalence show how in sexual reproduction 

 the offspring resemble their ,,pareuts", while differing from them. 

 The likeness in the primary germ-cells leads to likeness in the offspring, 

 and along with this unlikeness is bound to come in. For the primary 

 germ-cells themselves give rise to secondary germ-cells, which have 

 lost their powers of independent development. It is these, and these 

 only as a rule, which are present in the finished embryo. They and their 

 progeny are never capable of normal independent development 1 ); but it 

 is their destiny to go through the process of reduction of chromosomes, 

 with the ensuing formation of ,,sexual products", or gametes, eggs 

 and spermatozoa. Here, as is of course now generally recognised, 

 unlikeness enters. Although the egg or spermtraces its long ancestry 

 to one of a certain set of primary germ-cells, of which one also gave 

 rise to the ,,embryo" or form, whose ,,offspring", according to social 

 and commonly accepted ideas, the egg or sperm itself was, this said 

 egg or sperm unites with another sperm or egg, the ,,offspring" of a 

 different individual, which in its turn with its reproductive elements 

 traces a similar origin and ancestry from another set of primary germ- 

 cells. With the union the new cycle begins. 



It is thus that the formation of primary germ- cells underlies the 

 fundamental facts of heredity and explains these. And it is thus without 

 their knowing it, that the formation of primary germ-cells at a certain 

 epoch of the development, prior to the production of the embryo, is 

 the real basis of Wei smann's finds in heredity, and, to a still greater 

 degree, of those, associated with the name of Gait on. 



The application in detail of the results to the phenomena of here- 

 dity is beyond the scope of my researches. To indicate the way may 

 suffice. 



Galton has been led by his studies and researches on inheritance 

 to what is known as Gal ton's law 2 ). According to this law, ,,the 

 two parents between them contribute on the average one-half of each 

 inherited faculty, each of them contributing one quarter of it. The 



1) In the Vertebrata! 



2) Francis Galton, The average Contribution of each several Ancestor 

 to the total Heritage of the Offspring. Proc. Roy. Soc. Lond. Vol. 61, 

 p. 401408, 1897. 



