SEXUAL SELECTION 451 



from the large number of fishes of which the males are 

 either permanently or periodically brighter than the females, 

 but whose life is not at all more important for the welfare 

 of the species than that of the female, this view can hardly 

 be maintained. When we treat of birds we shall meet with 

 analogous cases, where there has been a complete inversion 

 of the usual attributes of the two sexes, and we shall then 

 give what appears to be the probable explanation, namely, 

 that the males have selected the more attractive females, 

 instead of the latter having selected, in accordance with 

 the usual rule throughout - the animal kingdom, the more 

 attractive males. 



On the whole, we may conclude that, with most fishes 

 in which the sexes differ in color or in other ornamental 

 characters, the males originally varied, with their variations 

 transmitted to the same sex, and accumulated through 

 sexual selection by attracting or exciting the females. In 

 many cases, however, such characters have been transferred, 

 either partially or completely, to the females. In other 

 cases, again, both sexes have been colored alike for the 

 sake of protection; but in no instance does it appear that 

 the female alone has had her colors or other characters 

 specially modified for this latter purpose. 



The last point which need be noticed is that fishes are 

 known to make various noises, some of which are described 

 as being musical. Dr. Dufoss^, who has especially attended 

 to this subject, says that the sounds are voluntarily pro- 

 duced in several ways by different fishes: by the friction 

 of the pharyngeal bones — by the vibration of certain muscles 

 attached to the swim-bladder, which serves as a resounding 

 board — and by the vibration of the intrinsic muscles of the 

 swim-bladder. By this latter means the Trigla produces 

 pure and long-drawn sounds which range over nearly an 

 octave. But the most interesting case for us is that of two 

 species of Ophidium, in which the males alone are provided 

 with a sound-producing apparatus, consisting of small, 

 movable bones, with proper muscles, in connection with the 



