556 MR. J. B. SUTION ON ATAVISM. [ Dee. 21, 
secondary sexual characters can be explained on the principle known 
as the “ Correlation of Organs.” 
In order, however, to render this explanation tenable, it will be 
absolutely necessary to prove, as far as possible, that the germs of 
secondary sexual organs, which only manifest themselves occasionally 
in the females of dimorphic forms, are really inherited ; and, if the 
female is furnished with the germs of these structures, to show by 
what method they are transmitted. It is to this somewhat intricate 
part of the question that we niust now direct our attention. 
If a careful analysis be made of those structures which constitute 
secondary sexual characters, we shall find that they are almost entirely 
developed in connection with the integument. The majority— 
whether they be horns, bristles, spurs, or teeth, for attack or defence ; 
or exuberance of hair, feathers, wattles, combs, &c., for esthetic 
purposes,—the integument and the immediately subjacent tissues are 
responsible for them. 
In the earliest embryos of most mammals we distinguish at a 
very early stage two layers of cells, known as the epiblast and hypo- 
blast. In most of the Metazoa a new layer is interposed known as 
the mesoblast ; this originates in part from the epi- and in part from 
the hypoblast. It is the epiblast and the portion of mesoblast 
immediately adjacent that furnishes secondary sexual organs. From 
whence is the epiblast derived ? 
-. We know new that the essential act of impregnation consists in 
the union of a spermatozoon with an ovum; the head of the 
spermatozoon constitutes the male pronucleus, the germinal area the 
female pronucleus. After the pronuclei have united segmentation 
begins, and the formation of the fundamental layers is quickly brought 
about. ‘There are good grounds for believing that the initial streak 
indicating the commencement of segmentation really marks the line 
of fusion between male and female pronuclei. 
If we measure the size of the head of a functional spermatozoon, 
it will be found equal to ,),5 of an inch, whereas the germinal 
area of the ovum equals =, of an inch. It is a very significant fact 
that the segments which give rise to the epiblast are smaller than 
those which furnish the hypoblast and mesoblast; to this there are 
very few exceptions. This is exactly what might be expected, the 
halves of a globe z=; of an inch in diameter would certainly be 
smaller than the halves of a sphere one twelfth the size. 
The facts at our disposal seem to point to the conclusion that the 
epiblast is chiefly derived from the male element, while the female 
pronucleus is responsible chiefly for the hypo- and greater portion of 
the mesoblast. 
If this be true, the transmission of characters peculiar to the male 
is not so obscure as many have supposed. 
We must now inquire howit is, that if the female possesses all the 
secondary sexual characters of the male in a latent manner, what is 
it that prevents them manifesting themselves. 
When differentiation of sexes occurs in animals previously 
hermaphrodite, it involves either the loss of certain characters on the 
