Fish as Nest-builders. 



from time to time he enters to make sure that all is 

 well withki, vibrating his fins the while so as to pro- 

 duce a current of water through the nest to aerate the 

 spawn. All this time the mothers take not the least 

 heed of what is going on ; in fact, they are conspicuous 

 by their absence from this scene of domesticity, having 

 gone off to enjoy themselves, and it is the industrious 

 little male who brings up the family. Indeed, should 

 some accident overtake him during his guardianship, 

 the nest will at once be torn to pieces by other Stickle- 

 backs and its precious contents devoured. The parental 

 labours do not terminate with the hatching of the spawn, 

 for the male keeps his offspring safely confined to the 

 nest for about a* week after their hatching, until they 

 have grown to about three or four millimetres in length, 

 when he pulls the nest to pieces and permits his family 

 to come forth. 



The marine Stickleback, sometimes called the Sea- 

 adder, is rather larger than the fresh-water species, 

 attaining to a length of from six to eight inches ; and 

 not only does it build a nest, but it binds the materials 

 together with silky threads spun from its own body. 

 " The nest," writes Professor J. T. Cunningham, " con- 

 sists of growing seaweeds, and the kidneys of the male 

 in the breeding season secrete a gelatinous substance 

 which hardens as it is drawn out into a strong, white, 

 continuous fibre, and this is wound about and woven 

 into the nest as the fish swims about it during its con- 

 struction. This fish, therefore, may be said to spin 

 a cocoon somewhat in the same manner as a silkworm 

 or other caterpillar. The sea Stickleback affords the 

 only instance of spinning among the vertebrates of 



59 



