586 
GEOFFEEY SMITH. 
istic of the species. In these cases, althougli a certain 
amount of sperm was always present as well, the female part 
of the hei’inaphrodite gland greatly preponderated. Here, 
then, we have individuals of hermaphrodite constitution, 
which normally only show the male characters throughout 
life, i.e. in which maleness is dominant; but when the 
presence of the parasitic Sacculina sets up a distm-bance 
this dominance is almost completely reversed, and the hitherto 
recessive female characters appear in all completeness. 
Again, to take the opposite case. In deer and pheasants it 
is well known that certain individuals which have actually 
bred as females, may in old age develop the male secondary 
sexual characters in a very complete manner. Such indi- 
viduals prove themselves to have been heterozygotes in which 
the dominant female character is replaced for some reason by 
the recessive male. 
It is clear, therefore, from the foregoing' instances, that 
individuals of hermaphrodite constitution may exhibit any 
of a whole series of modifications from apparently pure male- 
ness, through simultaneous hermaphroditism, to apparently 
pure femaleness. This being the case, the difficulty of con- 
sidering that in a normally dioecious animal either one 
sex or the other is a sex-hybrid, according to the species or 
group of species we are dealing with, is materially lessened. 
We may, in fact, state the case as follows : that three types 
of individuals exist in respect of sex, pure males, hermaphro- 
dites, and pure females, and that the hermaphrodites may 
appear as males, hermaphrodites, or females according to a 
physiological condition which is confessedly not understood. 
We have, so far, formulated the Mendelian theory of sex, 
so as to account for the existence within a species of indi- 
viduals having' either the constitution $ and $ ? or of 
? and c? c? j in the former case maleness being dominant, 
in the latter femaleness. This is the simple half-hybrid 
theory of sex. We must, however, consider the possibility 
of the existence of three types of individuals within the same 
species, viz. J* c? > c? ? > and $ ? . The diflSculty of this 
