14 



the north and the autamn migration to the north (east coast of 

 Britain, north of the Wash). With increase in size the outward 

 migration is still further to the north and into deeper water. 



5. — Coming maturity impels the fish to migrate in winter 

 contranatantly to a still greater distance from which it will return 

 with the spawning migrants. It is probable if not on the first 

 occasion at some succeeding season the outward migration may 

 be such as to associate the fish with spawners of a region related 

 to another school. So far as is known this is usually if not always 

 in the contranatant direction. 



6. — After spawning the spent fish join the summer denatant 

 migrants and migrate later than these and evidently further than 

 these for winter. 



If the contention be admitted that the schools owe their 

 origin — and there does not appear to be any other explanation — 

 to the showering of the yomig on the ground in a region which 

 must bear an average relationship to the spawning ground on 

 the one hand and to the summer feeding ground on the other, it 

 follows that if we knew the factors, the history in this and similar 

 cases could be completely stated. We do not yet know the 

 spawning ground of each of the schools, the normal period of 

 pelagic life, the region where the demersal fry are mainly con- 

 gregated in each case, and the mean rate of the current during the 

 spa waning season in different regions. 



Note. — In this and the following papers dealing with migrations, two 

 words with their variants are introduced to express migrations with refer- 

 ence to current. They were suggested by my colleague, Professor J. Wight 

 Duff. Denatant is applied to migrations with the current, and contranatant 

 to migrations against the current. 



In the sea particularly the eggs and the larvae or the larvss alone are 

 rotated by the tidal currents, and at the same time carried passively in a 

 definite direction by the oceanic current. The path may be represented 

 by a spiral beginning over the spawning gromid and ending at the recruiting 

 gromid. This passive denatant drift is succeeded by the seasonal and the 

 spawning contranatant and denatant migrations. The use of the terms 

 will be clear from the above paper and figures 4 — 6. * 



* 1915, Meek, " Nature," p. 231 (April 29th). 



