lV NORMAL HERMAPHRODITISM 105 
Normal Hermaphroditism in Cirripedia and Isopoda 
Epicarida. 
The above-mentioned groups contain the only normally 
hermaphrodite Crustacea, and since they are in most respects 
highly specialised, we may be certain that they have been 
secondarily derived from dioecious ancestors. They both lead 
a sessile or parasitic life, and it is noteworthy that this habit is 
often associated with hermaphroditism, e.g. in Tunicates. A 
sessile or parasitic mode of life is one in which the metabolic 
functions are vegetative and assimilatory rather than actively 
kinetic or metabolic. It is in this state that we have seen the 
males of a number of Crustacea taking on a temporary or partial 
hermaphroditism. We may, therefore, inquire, whether in these 
eases of normal hermaphroditism there is any evidence to show 
that here too the hermaphroditism has been acquired by the 
male sex as a response to the change in the metabolic conditions. 
In the parasitic Isopoda Epicarida (see pp. 129-136) the herm- 
aphroditism is of a very simple kind; all the individuals are at 
first males, whose function it is to fix on and fertilise the adult 
parasites. These subsequently develop into females which are in 
their turn cross-fertilised by the young larvae derived from 
a previous generation. All the individuals being alike, it seems 
probable that they have been derived from one sex, and the 
general nature of hermaphroditism deduced above may lead us 
to suppose that that sex was originally male, the female having 
been suppressed. In certain Cirripedia, eg. most species of 
Scalpellum, there exist, besides the hermaphrodite individuals, 
complemental males, so that here a superficial conclusion might 
be drawn that the hermaphrodites represent the female sex. 
But if we can suggest that the complemental males are in 
reality similar in derivation to the hermaphrodite individuals, we 
shall be in a position to claim that the hermaphrodite 
Cirripedes are similar to the Isopoda Epicarida, and have 
probably also been derived from the male sex. There is decided 
evidence pointing to this conclusion. In the first place, the 
complemental males of at least one species of Sca/pellwm, WN. 
peronii, do show an incipient hermaphroditism! in the presence 
1 Gruvel, Monographie des Cirrhipédes, 1905, p. 152. 
