136 HABITUDES AND ATTITUDES 



optimum. For three days after hatching the 

 larvae remain at the surface, floating on one side 

 with yolk - sac well up. Before hatching, the 

 body of the embryo encircles about two-thirds 

 of the equatorial region of the yolk like a belt ; 

 the tail then twitches, the vitelline membrane is 

 ruptured, and the larva with its yolk-sac is set 

 free. 



The floating eggs of these tropical fresh-water 

 fishes are not comparable with the hyaline 

 pelagic eggs of many marine fishes because they 

 do not move from the nest ; their buoyancy is part 

 of the method of nidification and brooding, not 

 a means of dispersal. I do not know any other 

 instances of eggs of fresh-water fishes floating at 

 the surface of the water by their own buoyancy ; 

 but the same advantages proximity to atmos- 

 pheric air and to sunlight are secured in other 

 ways, as by attachment to aquatic plants, or by 

 deposition in very shallow water, or by special 

 methods of nidification, as in the floating nests 

 of Gymnarchus or the foam nests of Sarcodaces, 

 which were described by the late J. S. Budgett. 1 

 There would seem, however, to be points of closer 

 comparison between the eggs of the murral and 

 those of some marine fishes, namely, the weevers 

 (Trachinidae), according to the observations of 

 J. Boeke (1903). These eggs are maintained 



1 Cf. The Budgett Memorial Volume, edited by J. Graham 

 Kerr, Cambridge Univ. Press, 1907. 



