THE FLAT-FISH FAMILY 219 



necessary to consider different districts separately, on account 

 of the great differences in the size at which maturity is attained, 

 and consequently in the rate of growth. At Plymouth the smallest 

 mature females are 9 inches long, the largest immature less than 

 15 inches. The limits in length of the mature and immature 

 overlap one another in this way in -consequence of the fact that 

 all individuals do not grow at the same rate or become mature 

 at the same age. The corresponding limits observed at Grimsby 

 were 1 3 inches and 18 inches, so that there is a difference of about 

 4 inches between the sizes of plaice when they first become mature 

 in the Channel and in the North Sea. The limits for the males 

 are lower in both districts, but it is doubtful if the observations 

 made were sufficient to determine these limits accurately : they 

 were 9 inches and 13 inches at Plymouth, 9 inches and 16 inches 

 at Grimsby. The difficulty of distinguishing immature from 

 spent males is greater than in the case of females. 



It has been proved that the Grimsby limits hold good for 

 plaice throughout the area extending from the English coast to 

 the coast of Germany in an east to west direction, and from the 

 north of Scotland to the Texel in a north to south direction. 

 But along the Dutch coast as far north as the Texel the small 

 Channel plaice extend, the limits of maturity and immaturity 

 being the same in this region as on the fishing grounds off 

 Plymouth. 



I have made one experiment, not a very extensive one, on 

 the growth of plaice in the Aquarium at Plymouth. In July, 

 1893, seven specimens whose lengths varied from 2\ to 3f inches 

 were put into a tank. They were captured at sea, and believed 

 with good reason to belong to the brood of the year, that is, to 

 have been hatched in the preceding spawning season between 

 January and March. In the following October these specimens 

 measured 2f to 5| inches. In April, 1894, when they were one 

 year old, one of them measured 6| inches. In December, 1894, 

 when they were nearly two years old, the only two surviving 

 were r j\ inches and 8^ inches in length. These fish were kept 

 in a tank only 5 feet in length and \\ feet deep, and the number 

 of them was too small to afford evidence of the average rate of 

 growth. But a direct observation of this kind is of great use as 

 a guide in drawing conclusions from the sizes of specimens taken 

 from the sea. 



