]V NORMAL lIEKMAPIIKOnrriSM IO5 



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 hal'ii i> 

 often associated with hermaphroditism, e.<j. in Tunicates. A 

 sessile or parasitic mode of life is one in which the metabolic 

 functions are vegetative and assimilatory rather than act i\ fly 

 kinetic or metaholic. It is in this state that we have seen the 

 males of a number of Crustacea taking on a temporary or partial 

 hermaphroditism. AVe may, therefore, inquire, whether in these 

 cases of normal hermaphroditism there is any evidence to sh\\ 

 that here too the hermaphroditism has been ;ici|iiired by thf 

 male sex as a response to the change in the metaliolic conditions. 

 In the parasitic Isopoda Kpicarida (see pp. 1J 9- !:'(>"! the herm- 

 aphroditism is of a very simple kind: all the indhiduals ;uv at 

 lirst males, \\lmse 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 seem^ 

 probalile that they ha\e been derived from one se\. and the 

 general nature of hermaphroditism deduced above may lead us 

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

 lireu suppressed. In certain t 'irripedia, <'.;/. niost speeie> of 

 Si;i/f>,-//i/itt. there exist, besides the henna phrodile individuals, 

 eomplemental males, so that here a superlicial conclusion might 

 l>e drawn that the hermaphrodites represent the female se\. 

 I'.ut if we can suggest that the complemetital males air in 



reality similar in derivation to the hermaphrodite individuals, we 



shall be in a position to claim that the hermaphrodite 

 ('irripedes are similar to the Isopoda Kpicarida, and ha\r 

 probably also been derived from the male sex. There is decided 

 evidence pointing to this conclusion. In the lir<t plaee, the 

 COmplemental males of at least one species of S<-nIi>,-l! n 111. N. 

 j-i-iiii, do show an incipient hermaphrodil ism ' in the presence 



1 (ini\rl. Monographic des Cirrhipedes, I'.HI;.. p , 



