HATCHING. 43 



intervals ; but about the fifth day from the general 

 hatching out of that batch of eggs, a general desire to 

 hide becomes manifest. Accordingly in every angle 

 of the trough, except* where the water is disturbed by 

 the stream falling in from the trough above, there will 

 be seen a writhing, wriggling mass of alevins, each 

 trying with might and main to hide itself under its 

 neighbours, all heads directed towards the corner, and 

 the strongest youngsters lying in it, until forced out by 

 superior numbers ; and this goes on for some time, it 

 may be a fortnight or three weeks, according to the 

 temperature of the water. During this time the alevins 

 will have gained greatly in size, grace and symmetry. 

 They will have become wonderfully active, swimming 

 rapidly up and down the tube, and their fins will be 

 seen to have grown, and the tail developed to a sur- 

 prising extent. The umbilical sac or vesicle, too, will 

 have half, or more than half disappeared, having been 

 gradually absorbed during this period, to yield the 

 necessary nourishment for the evolution of the various 

 organs of the fish, which were at first in a rudimentary 

 state. 



After this they gradually separate, leaving the cor- 

 ners of the trough and covering its whole length at 

 pretty even distances, having the appearance, at a 

 distance, of extra thick black pins. They do not move 

 much now ; however, on looking over them a few will 

 be seen in motion at intervals ; but it can scarcely be 

 realized that these seemingly impotent creatures will, 

 in a week or two, be in incessant motion ; yet such is 

 the case, as the rest appears to be needed for the com- 

 plete development of the swimming apparatus ; when 

 this is duly furnished, they will be seen to rise spon- 



