611 
1908-9.] Mendelian Action on Differentiated Sex. 
mass, just as the female zygote gives off the primitive germ-cell mass ; and 
from these, as stated in 3, the gametes arise. 
The history of the development of this view of the zygotic origin of the 
gametes and its long neglect are of great interest. 
O C5 c5 
Owen in 1849 made a remarkable observation. In his well-known 
paper on parthenogenesis he stated that “ not all the progeny of the 
primary impregnated germ cells are required for the formation of the body 
of all animals : certain of the derivative germ cells may remain unchanged 
and become included in the body which has been composed of their meta- 
morphosed and diversely combined or confluent brethren : so included, any 
derivative germ cell or the nucleus of such may commence to repeat the same 
process of growth.” This was a striking observation, and it is the irony of 
investigation that this epoch-making observation should have been neglected 
for more than half a century while his contribution to parthenogenesis, still 
an obscure and doubtful theory, should alone have attracted great attention 
and been constantly quoted. It was only in 1891 that Eigenmann inde- 
pendently described the same phenomenon in Cymatogaster segregatus and 
thus confirmed Owen’s work. Since then observations have been fairly 
numerous and important. Balbiani, Boveri, Beard, F. A. Woods, Ingalls, 
and others have substantiated and extended Owen’s discovery in their views 
of the continuity of the germ cells. Ingalls’s observation is of importance, 
as the primitive germ cells in a 4’9 mm. human embryo were found, not on 
the Wolffian ridges, but en route for them and arrested at the root of the 
mesentery beneath the coelomic epithelium. Beard especially has demon- 
strated and fought for this view. 
This origin of the germ ceils first shown by Owen may be combined 
with Weismann’s great generalisation of the continuity of the germ plasma 
under the term of the Owen-Weismann law, or continuity of the germ cells. 
This means that the gametes are a reduced part of the primitive germ cells, 
these arising from the primitive germ -cell mass, a non-reduced portion of the 
original zygote. The gametes are thus directly zygotic in their origin, are 
not derived from somatic cells, and they thus carry on the race pure and 
not influenced by the “ soma ” proper. 
This being the nature of the gametes, we have now to consider if we 
can in any way find out how the determinants of heredity, using this term 
in a general sense, are allotted to the dimorphic gametes. What contribu- 
tion does each gamete bring to the zygote it helps to form ? 
For this purpose a source of information is present which has been 
ignored by almost all observers with the exception of Wilms and Beard, 
viz. ovarian and testicular dermoids and the dermoids found elsewhere in 
