LOVE-MAKING AMONG FISHES 177 



opening is covered by a special scale, which is free on 

 one side, left or right, and not on the other. Thus 

 copulation is possible only from the side, and a left-sided 

 male can only conjugate with a right-sided female, and 

 vice versa. Here is one of the most extraordinary cases 

 of specialized secondary sexual characters known. How 

 do the sexes distinguish their complemental mates ? 

 It is important that they should, for unions are otherwise 

 impossible. 



In the Dragonet (Callionymus lyra) the male differs 

 conspicuously from the female in being much the larger 

 — an exception to the rule — and in having the fin-rays 

 enormously elongated. Further he wears a conspicuously 

 resplendent livery, but this is strictly a " nuptial " livery, 

 the colours waning as soon as the period of sexual activity 

 is past. That these colours play the same part as with 

 the birds is clear from the observations of the late Saville 

 Kent. " The male," he says, " resplendent in his bridal 

 livery, swims leisurely round the female, who is reclining 

 quietly on the sand, his opercula distended, his glittering 

 dorsal fins erect and his every effort being concentrated 

 upon the endeavour to attract the attention of his mate. 

 . . . The female, at first indifferent, becomes at length 

 evidently dazzled by his resplendent attire and the per- 

 sistency of his wooing. She rises to meet him, the pair — 

 so far as is practicable with fishes — rush into each other's 

 arms, and with their ventral areas closely applied, ascend 

 perpendicularly towards the surface of the water." In 

 the course of this ascent the ova and sperms are shed, 

 and fertilization takes place. 



The difficulties in the way of the study of the behaviour 

 of fishes during the critical period of mate-hunting are 

 many and obvious. Something may be inferred from the 



