NORMAL HERMAl'lIRODITISM I05 



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. xA. 

 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 

 cases of normal hermaphroditism there is any evidence to show, 

 that here too the hermaphroditism has been acquired hy 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 indivichials are at 

 first males, whose function it is to fix on and fertilise the adult 

 parasites. These sul)sequently 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 Ijeen derived from one sex, and the 

 general nature of hermaphroditism deduced above may lead us 

 to suppose that that sex was originally male, tlie female having 

 lieen suppressed. In certain Cirripedia, e.g. most species of 

 ScaljJellurii, there exist, besides the hermaphrodite individuals, 

 complemental males, so that here a superficial conclusion might 

 be drawn that the liermaphrodites 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 hermay)hrodite 

 Cirripedes are similar to the Isopoda Epicarida, and have 

 proljably 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 Scalpellum, X 

 2)eronii, do show an incipient hermaphroditism ^ in the presence 



^ Griivel, Moiwgraphk dcs Cirrhqjklcs, 1905, p. 152. 



