FISHES 217 



Cyclopterus lumpus the relative sizes are reversed. In Cal- 

 lionymus we have seen that the male has to make greater 

 exertions in the breeding process, and if it is true that the 

 male Cyclopterus remains attached, by means of his ventral 

 sucker, beside the spawn he has fertilised, this sedentary duty 

 may well be the cause of his diminished proportions. The 

 female has the sucker equally well developed, but as she does 

 not assist in guarding the spawn, she is probably more active, 

 and also probably obtains more food. 



The nest-building habits of the Sticklebacks have often 

 been observed and described, and these fishes seem to afford 

 a case in which the relation between habits and sexual 

 dimorphism can easily be studied. Considering that the 

 male alone builds the nest, courts the female, and keeps 

 guard over the nest and eggs, driving off intruders with great 

 vigour and courage, it might be expected that he would show 

 striking differences from the female in some of his structural 

 characters. But, so far as I can discover, this is not the 

 case. The characters of the fresh-water form, Gasterosteus, are 

 very variable, so that several varieties have been described, 

 and, by some naturalists, distinguished as species, but it does 

 not appear that these differences are sexual. The chief dis- 

 tinction of the male in the breeding season is the assumption 

 of a bright pink or red colour on the lower part of the head 

 and the ventral surface of the body. The females are rather 

 dull coloured. 



What then exactly are the habits and behaviour of the 

 fish ? The males are described as very pugnacious. In fight- 

 ing they swim round each other like boxers or swordsmen, 

 and then one dashes at the other and tries to strike him with 

 his spines. Of these it has two to four on the back, represent- 

 ing the anterior rays of the dorsal fin, and one on each side 

 representing the pelvic fin. These spines are firmly hinged 

 to bony plates in the body, and the sides of the body are pro- 



