342 



THE INVERTEBRATA 



degenerate males, the large individuals are without testes, so that the 

 sexes are separate. The function of the complemental males is 

 probably the effecting of cross-fertilization, for the species which 

 possess them are of solitary habit. The phenomenon perhaps arose 



scu, ytgm. 



- - cnl. 



Fig. 246. Cirripedia Thoracica. A, Lepas anatifera. B, Balanus. C, Scal- 

 pellum vulgare. D, Male of the same, enlarged. A-C, after Darwin; D, after 

 G. Smith, cna. carina ; cnl. carinolateral ; e. vestige of eye ; la. lateral ; op. open- 

 ingof mantle cavity ; rst. rostrum ; y^^/. rostro lateral ; scu. scutum ; ^i/e. peduncle ; 

 t. testis; tgm. tergum; ^, dwarf males. 



from the settling of young hermaphrodite individuals on the stalk 

 of old ones, which is common in stalked barnacles. 



Balanus (Fig. 246 B), the common acorn barnacle, differs from 

 Lepas in the lack of a stalk, and in having an outer wall of skeletal 



