612 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
the body. I take up this question in regard to ovarian dermoids with 
which I am familiar, but shall add some remarks in regard to the less common 
testicular dermoids. 
The ovarian dermoid is a quite common and familiar tumour. It is 
usually cystic, and contains a creamy fluid often like salad dressing, and 
may have hair, teeth, brain, brain tissue, alimentary canal — in fact, samples, 
as it were, of all the germ layers, and not mainly of the ectoderm, as is 
usually urged. There is occasionally a more or less solid form, the teratoma ; 
and this, as Wilms pointed out, is usually an imperfect anterior part of an 
embryo. Wilms and others have shown that the tissues are normal in 
structure. A very important teratoma removed by operation by Culling- 
worth and examined by Shattock is a most remarkable specimen. It is 
preserved in the Hunterian Museum, London, and is well worth a visit. 
Two limbs are present, and a peritoneal cavity with a blind coil of intestine. 
There is a short rudimentary spinal column with a pelvic girdle, and in each 
of the lower limbs there is an osseous element filled with fatty marrow. 
Between the limbs are two distinct labia, between these a distinct depression, 
and behind them a perineal raphe. 
I must next draw attention to a very important fact as to all dermoids, 
viz., they contain no evident genital organs proper, and, so far as any 
observer has as yet noted, no microscopical elements pointing to their 
distinct existence. There is no doubt as to such teratomata not being the 
product of immediate fertilisation, as they are found in virgin women, and 
I have, like other operators, removed them from children before puberty. 
How, then, do we get such remarkable productions ? I have already stated 
that the primitive germ cell is a zygote owing to its origin, and must contain 
an id : the gamete is a reduced primitive germ cell. A primitive germ cell 
can therefore form an embryo, but never does so, owing to its apparently 
constant reduction to a gamete and its loss of the power of zygotic develop- 
ment. If, however, a gamete has a certain number of determinants and is 
imperfectly reduced, it may retain the power of zygotic development and 
thus form part of an embryo. 
Now in the ova I have suggested that we have two kinds, a sex ovum 
and a non-sex ovum ; and for the reasons already given we may consider a 
teratoma as a non-sex ovum which by an imperfect reduction has retained 
the power of zygotic development not normally possessed by a gamete. 
The teratoma never contains all the parts of the anterior part of an 
embryo; and this is significant, as we shall see. 
The same applies to testicular teratoma. In a recent paper Okhubo 
analyses the cases in the Prag collection, 11 in number, and also 107 
