1908-9.] Mendelian Action on Differentiated Sex. 613 
other cases in literature, and to his valuable paper I must refer those 
interested. 
Before stating an explanation of dermoids, I may mention that chorio- 
epitheliomata, the malignant tumours associated with the hydatid mole, 
have been found in teratomata by Schlagenhaufer, Ritchie, and others. 
Many views have been brought forward as to the origin of teratomata, 
and the one I advise as a working theory is that it is derived from a non- 
sex male or female gamete which has retained its power of zygotic develop- 
ment. The facts already stated as to the primitive germ cells passing after 
their formation from the P.G.C. mass by the yolk-sac and blastoderm into 
the embryo and their occasional arrest en route , helps one to understand 
their rare position outside the ovary and testis. 
If thus a teratoma like Shattock’s is the anterior part of an embryo, i.e., 
in the main somatopleuric, and if it arises from a non-sex ovum, this makes 
the non-sex ovum contain the determinants of the somatopleuric part and 
the sex ovum the determinants of the genital organs and other parts of the 
splanchnopleure. This supports the popular belief that boys get brain and 
body from and through the mother, their sex and splanchnopleure through 
the father. The converse holds good for girls. A teratoma is only fart of 
the anterior part of an embryo ; but this is not inconsistent with the above 
supposition, and indeed boys do not follow the mother and girls the father 
fully in the respects defined above. This means that the father also contri- 
butes in part to the boy’s somatopleuric element, the mother to the girl’s. 
I think this line of inquiry as to teratomata very promising, and that a 
particularly full examination should be made of all suitable specimens. 
The human zygote, male and female, contains the determinants, inter 
alia, for the potent and non-potent organs. Thus, sex has differentiated 
from a hermaphrodite condition away far back in the invertebrata. 
Mendelism acts on differentiated sex, and is evident owing to the difference 
between the potent and non-potent organs. 
The potent and non-potent determinants are, however, combined and 
inseparable in the human zygote, and thus in twinning of one zygote we 
always get an equal division of sex determinants. 
It is different in some animals, and in black cattle we get male twins, 
one potent and the other sterile — the free-martin. In the potent twins the 
potent sex determinants have been segregated ; in the free-martin, the non- 
potent ones. Thus we may arrange the relations of sex differentiation to 
the Mendelian scheme as follows : — 
