207 



left side. The pigmentation now gradually disappears 

 from tlie lower side. 



The larvae now feed almost entirely on Copepoda, 

 with which their stomachs are usually crowded ; larval 

 Molluscs and larval Crustacea are also eaten. After the 

 metamorphosis the food is changed, and the small fishes, 

 1| to 4 inches, feed largely on various Annelids such as 

 Nereis and Pectinaria, on small Crustacea such as Mysis, 

 and various Amphipods and small Crangons. Later on 

 the fish adopts its definitive food, which is niostl}^ Mol- 

 lusca, the favourite forms being Cardium, Tellina, Mactra, 

 Scrobictdaria, Donax and MytUus. The character of the 

 food changes little during the rest of its life. 



Rate of growth. — A variable time is taken up by the 

 changes above described, which were observed in larvse 

 kept in aquaria. For instance, although the Plaice in 

 the Danish seas may spawn as early as November, no 

 larvae of 12mm. length are taken there till May. They 

 therefore require six months to pass through the meta- 

 morphosis. Two methods have been adopted for esti- 

 mating the rate of growth subsequent to the larval period. 

 The most obvious one is to keep a large number of young 

 fish in captivity in aquaria, and to observe for as long a 

 period as may be possible the changes in body length. 

 This method is evidently open to the grave objection that 

 the fishes live under artificial conditions, and these may 

 influence their rate of growth. The other method is to 

 fish often in waters which contain great numbers of Plaice 

 of different sizes, and to deduce the growth rate from the 

 grouping of the individuals of different lengths. When 

 this is done and the results of measurement of all the 

 fishes captured are tabulated, it is seen that those captured 

 at any one time may be arranged into several groups in 

 each of which the greater number are grouped round cer- 



