1897- SPAWNING HABIT OF TELEOSTEAN FISHES. 385 



Fig. 



which shows the relations of floating eggs to be markedly different 

 from those of drifting inanimate objects. Broadly speaking, however, 

 it is only when the yolk-sac has become absorbed and the post-larval 

 stage has been entered upon that the little fish is capable of active 

 movement, and can then, to some extent, perform its own migrations. 

 Taking then a typical case of a certain species, with a pelagic 

 spawning-habit, the eggs will be laid offshore in the surface-water and 

 will be subjected during their development to a pelagic drift, which, 

 in the great majority, will be shorewards. The direction of this drift 

 will be determined by that of the prevalent winds at the particular 

 season, and its duration will depend upon the length of time it takes 



for the post-larval stage to be reached 

 and the drift-current to be forsaken. 

 In the accompanying diagram (Fig. i) 

 the point A represents the spawning- 

 area of the species under considera- 

 tion, and the resultant pelagic drift is 

 in the direction from A to D, at which 

 latter spot the young forms descend 

 to the bottom. It is obvious that this 

 drift can be resolved into a drift A C 

 parallel to the shore and a drift A B 

 at right angles to it. In different 

 areas the comparative magnitude of 

 these two components may vary to any extent; but by the time the 

 adult stage is reached there must be a return to the point A, by a 

 compensating migration of the young forms, or the area would be 

 annually depleted of the species. 



In the case of the North Sea, in the east coast of Scotland area, 

 experiments with marked plaice have shown that they slowly migrate 

 northwards parallel to the coast before moving out to the spawning- 

 grounds.^ Independent observations with drift-bottles tend to show 

 that many of the eggs of the plaice laid off the east coast are drifted 

 southwards in their course.^ In other words, if in Fig. i the top of 

 the diagram be taken as north, A D will represent the course taken by 

 these eggs of the plaice, and the young plaice are found to migrate 

 from D to B along the coast and then outwards to A. There can be 

 httle doubt that the two are correlated phenomena. The extent of 

 the drift A C will depend upon the rate of the current, and upon the 

 time during which it acts upon the eggs and larva, but as the drift 

 in this direction can be compensated for, and its lengthening or 

 shortening is apparently not attended by fatal consequences, we may, 

 for the moment, neglect it and consider the drift in the direction A B, 

 assuming in our particular instance that A C=o, or that the eggs are 

 drifted directly inshore. 



1 T. W. Fulton, Rep. Fish. Board, Scotland, xi., p. 186, 1893. 



2 T. W. Fulton, Op. cit., xiii., p. 158, 1895. 



