6. General discussion. 37 



their taking up a position on other individuals of the same species. They do this, not as a 

 special adaptation for securing cross- fertilization, but owing to the retention of an instinct 

 which is no longer of any essential use to the species, except in so far as it lies at the basis 

 of the gregarious habit. This instinct was derived in the following way : the Cirripedes were 

 originally dioecious, the male being fixed upon the female, as in Scalpellum velutinum, the 

 Abdominalia etc. The male sex then acquired protandric hermaphroditism, the female sex 

 being suppressed and fertilization occurring much as in the Epicarida, namely by the larvae 

 (functionally males) fixing on the adult hermaphrodites (functionally females) . Then a shifting 

 of the time of sexual maturity occurred, the male and female products maturing at the same 

 time in the adult state, and in the majority of forms the instinct of fixation on the herma- 

 phrodites for fertilization possessed by the larvae was entirely given up and converted into 

 a general gregarious instinct instead. But in certain forms, viz. those with so-called comple- 

 mental males, the instinct still remains in the larvae more or less in its original state, and 

 this results in the fact that when they meet with an adult hermaphrodite at the proper stage 

 of development they fix themselves on it in the old position and are arrested in their develop- 

 ment, so as to appear as true males and not hermaphrodites as they really are. 



Finally there is nothing, either in the external or internal structure of the Cypris larvae 

 that fix themselves round the mantle-openings of Sacculinae, to make us suppose that they 

 differ from the ordinary Cypris larvae which affix themselves to crabs, in any other respect 

 than in the fact of their falling victims to a misguided instinct which all the larvae 

 equally possess. By following these lines of argument is it possible to obtain an explanation 

 of two of the most noteworthy characteristics of Cirripedes, firstly their gregarious habits, and 

 secondly their remarkable sexual variations together with the retention of an instinct long 

 after it has ceased to subserve its original function. But the full weight of the argument 

 can only be appreciated when the fundamental nature of hermaphroditism, as exposed in 

 Chapter 5, has been fully grasped and accepted. 



In contemplating this abortive male instinct and the curious results to which it leads, I see 

 in it another confirmation of the principles enunciated by the illustrious discoverer of comple- 

 mental males in Cirripedes, who first taught us completely that sublime aspect of Nature 

 which looks only to the preservation of the species and ignores the safety of the individual. 



And I do not think that we need be incredulous of the possible persistence of 

 dangerous and obsolete instincts, capable as we are of recognizing, if not in ourselves, at least 

 in other persons, the insistent development of instincts and habilitudes which, whatever 

 may have been their use in that state of nature to which they and certain theorists would 

 rapidly reconvert us, are inconsistent with the fulfillment of that destiny which civilization 

 or reason may persuade us to be ours. 



