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 

 cases 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 Epicaiida (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, e.g. most species of 

 Scalpelluni, 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 Scalpellnm, S. 

 peronii, do show an incipient hermaphroditism ^ in the presence 



' Gruvel, Monographic cles Cirrhipides, 1905, ]). 152. 



