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IIALF-GILLED FISHES 



or more stems of growing vegetation, and anchored fast. 

 Some observers say that the fish first brings a few stems and 

 bits of vegetation, and by means of his gelatinous secretion 

 practically ties them fast to the upright stalks, to use as a 

 foundation. 



The fish then proceeds to exude its secretion and dispose 

 it in commingling rings, vertically, around a space sufficiently 



TWO-SPINED STICKLEBACK. 



large for the female Stickleback to pass through. In a man- 

 ner nothing short of marvellous, a hood-like nest is spun, 

 of the fish's own secretion, which well retains its shape for 

 some weeks. In this the female deposits her eggs, all the 

 time jealously watched by the male, to prevent her from 

 eating them! The male guards the eggs until they are 

 hatched, and it is said that if the current flowing through 

 the nest does not meet his views as to strength, the fish in- 

 creases the volume of it by moving its pectoral fins to and 

 fro. Sticklebacks are sometimes kept in aquaria in order 

 that they may show their wonderful intelligence in nest- 

 building. 



