THE FLOUNDER FAMILY. 357 



the eggs of the plaice occurring in the surface-nets indicate 

 that the spawning-season of the food-fishes has begun. On 

 through February and March their numbers increase, and then 

 become less and less, until by the end of May they are of rare 

 occurrence, mostly at Smith Bank. As in other species, the 

 reproductive period of the plaice appears to vary considerably 

 in different localities thus Petersen and other observers in the 

 Danish waters find that this fish may even commence spawning 

 in November and December. In Sweden the spawning-season 

 is April, while at Heligoland, Ehrenbaum gives from January to 

 March. 



It seldom appears to spawn within the territorial waters, 

 unless where the bottom shelves rapidly into deep water, but 

 its eggs are found in great abundance with those of the haddock 

 some distance east of the Island of May and near the Bell Rock. 



The egg is pelagic and is of large size (see Table), the 

 mean diameter being about '069 inch or about 179 1 mm. 

 The egg-capsule exhibits a great number of minute punctures, 

 and its surface, in addition, is corrugated, having a sheen in 

 good light. There is no oil-globule. 



The plaice appears to be by no means so prolific as some 

 of its near allies, one female producing, on the average, about a 

 quarter-million eggs, though as many as 480,000 have been 

 recorded. The period of incubation is long, corresponding with 

 the early spawning-habit. Eggs fertilised in January at Dunbar 

 hatched in about 16 to 18 days, whilst those hatched here in 

 April had the period of incubation reduced to 8 or 9 days. 



These results are confirmed and extended by the recent 

 experiments of Dannevig at Dunbar. He found that within 

 certain limits the duration of the hatching-period could be 

 extended or curtailed at will by suitable variations in the 

 temperature of the surrounding medium. These results apply 

 with equal force in the case of several other species as well as 

 the plaice, and have an important bearing upon the questions 

 of distribution, the fate of the larvae and other points. 



In the eggs developed in April, the usual series of phenomena 

 give rise to the embryo, which on the seventh day is very 

 1 Ross's micrometer, St Andrews' scale. 



