86 



CRUSTACEA CIRRIPEDIA 



remarkable variation in the sexual constitution of some of the 

 species. The great majority of the Pedunculata and all the 

 Operculata are hermaphrodites, which habitually cross-fertilise 

 one another, and this they are well fitted to do, since they all 

 live gregariously and are provided with a long exsertile penis 

 for transferring the spermatozoa from one to the other. In 

 FiiUieipes, however, the individuals of which often live solitarily, 

 it appears that self - fertilisation may occur. In Scalpelluvi 



Fig. 55.--A, Complemental male of Scalpdhmi peronii, x 20 ; B, hermaphrodite 

 imlividual of & vnlgare, x 2. a, Complemental males, in situ ; b, rostrum. (A, 

 after Gruvel ; B, after Darwin.) 



three different kinds of sexuul constitution may occur: (1) 

 According to Hoek in K Icdanoides, taken by the Challenger, the 

 individuals are ordinary cross-fertilising hermaphrodites. (2) In 

 the great majority of species, including the common S. vulgare, 

 as originally described by Darwin, and since confirmed by Hoek 

 and Gruvel,^ the individuals are hermaphrodite, but there are 

 present affixed to the adult hermaphrodites, just inside the 

 opening of the valves in a pocket of the mantle, a varying 

 number of exceedingly minute males, called by Darwin "com- 

 plemental males." These tiny organisms are really little more 



^ Arch. Biol, xvi., 1899, p 27. 



