THE FLOUNDER FAMILY. 365 



to determine one of these factors, namely, the direction of 

 marine currents. Large quantities of sealed bottles were dis- 

 charged into the sea at the principal spawning-grounds and the 

 resultant effect of various currents was indicated by the final 

 destination of the bottles. The majority were washed ashore 

 in a general easterly and south-easterly direction, which would 

 lead us to suppose that from the spawning-grounds the pelagic 

 eggs, and even the larvae of the various fishes which frequent 

 those areas, are slowly borne along towards the shore, all having 

 a more or less southerly tendency. 



We can now perhaps obtain an insight into the significance 

 of the alongshore migration northwards of the young plaice, 

 alluded to above. It is evident that were there no such com- 

 pensating migration, the effect of the currents upon the eggs 

 and early stages of the species would slowly but inevitably 

 cause a transference of the species southwards. Further in- 

 vestigations, however, are necessary before definite conclusions 

 can be drawn. Another important effect of the pelagic spawning- 

 habit upon the distribution of the plaice is seen in the Danish 

 seas. The low specific gravity of the waters of the Baltic 

 opposes a barrier to the floating eggs of the plaice and its allies, 

 and only recently have a few of these been found to occur, deep 

 in the water, around Bornholme. 



The life-history of the plaice thus resolves itself into a cycle 

 of very definite limits, commencing with the pelagic egg fioating 

 over the spawning-grounds, the sport of wind and tide. Whilst 

 the development of the embryo proceeds within, the egg is 

 borne by the surface-currents towards the shore. The little 

 larvae continue, after hatching, to drift in the same direction 

 till, after an average duration of six weeks or so, the post-larval 

 fishes seek their way downwards through the mid-water to the 

 bottom, and in doing so, turn upon the left side. 



Close inshore, the little plaice, hidden in the sand or sandy 

 mud, grow rapidly and prosper, in company to some extent with 

 little flounders and dabs, and, as they become older they not 

 only migrate alongshore but move seawards with increasing 

 bulk till at last they complete their life-cycle by spawning and 

 launching their thousands of offspring upon the sea of life. 



