198 SEXUAL DIMORPHISM 



Saville Kent, 1 and is mentioned by Darwin. " Before the 

 breeding season both sexes were of a delicate silvery blue, 

 varied by irregular lines of pale yellow, a hue scarcely in 

 harmony with the popular name of ' Black Bream.' The light 

 colours disappeared in the breeding condition, or rather were 

 replaced by a prevailing shade of deep leaden black, deepest 

 on the back, but spreading over the whole surface of the fish, 

 except a few transverse lighter bands in the region of the 

 abdomen. The males in particular are most conspicuous for 

 this change, and these retiring from the remainder of the 

 shoal select certain separate and prescribed areas at the 

 bottom of the tank, where they commence excavating con- 

 siderable hollows in the sand or shingle by the rapid and 

 powerful action of the tail and lower portion of the body. 

 A depression of suitable size having been produced, each 

 male now mounts vigilant guard over his respective hollow, 

 and vigorously attacks and drives away any other fish of the 

 same sex. Towards his companions of the opposite sex his 

 conduct is far different. Many of the latter are now dis- 

 tended with spawn, and these he endeavours, by all the means 

 in his power, to lure singly to his prepared hollow, and there 

 to deposit the myriad ova with which they are laden, which 

 he then protects and guards with the greatest care. Whether 

 the aggregated produce of a large number of females is thus 

 consigned to one bed, and whether the ova are guarded by 

 the male until the young fish make their appearance, are 

 points which, while awaiting confirmation, may be almost 

 confidently inferred, reasoning from the very analogous nest- 

 forming habits of the Gasterosteidse." Raffaele, on the con- 

 trary, although he did not separately identify the eggs of 

 Cantharus lineatus, believes that those of this species, and 

 probably of all the species in the family, are pelagic. If this 

 be correct, the behaviour described by Saville Kent was only 



1 Nature, May 1873. 



