1895] Hermaphroditism in Animals. 531 
ontogeny repeats (to some extent at least) the phylogeny, we 
may logically conclude that the Hermaphroditism of those 
Metazoa, which present one or another of these phases of 
sexual development, has been secondarily acquired. This 
seems to me to be the only adequate explanation for such 
cycles of sexual development in the individual. Since the 
object of my present paper is only to discuss the meaning of 
these three kinds of Hermaphroditism, it would be irrelevant 
to bring into consideration the many other reasons tending to 
show that Hermaphroditism in the Metazoa is a secondarily 
acquired state. But this much may be remarked, that accord- 
ing to our argument all animal forms which present one or 
another of these phases of Hermaphroditism have been devel- 
oped from dioecious ancestral forms; and it must be left to 
future investigators to show in how many forms these phases 
are actually present, that is, whether or not all hermaphrodite 
Metazoa are either protandric, proterogynic, or successively her- 
maphrodite, and whether or not all hermaphrodite Metazoa are, 
therefore, to be regarded by the argument above as having 
been derived from dioecious ancestors. Finally in those forms 
where the individual is first male (or female), then becomes 
hermaphroditic, and lastly female (or male), we may conclude 
that the hermaphrodite species in question has not only been 
evolved out of dioecious ancestral forms, but is perhaps also — 
tending to become dioecious for a second time. 
There now arises the question: on which sex has the her- 
maphroditic state been superimposed? In the case of pro- 
tandric hermaphrodites, since here the male stage appears first 
in the ontogeny, one must suppose that it has been imposed 
on the male,—that ova have appeared in the testicle, and the 
individual has thus become hermaphroditic. Similarly, in all 
cases of Successive Hermaphroditism with perhaps the excep- 
tion of Microstoma lineare, we may consider that here too the 
Hermaphroditism has been superimposed on male individuals. 
In proterogynic forms, on the contrary, the Hermaphroditism 
has probably been imposed on the female, since here the 
female stage appears ontogenetically first. Pelseneer (37) 
while arguing that all hermaphrodite molluscan forms have 
a 
