

MA BINE BIOLOGICAL STATION AT PORT ERIN. 33 



is about \ of an inch (7 mm.) in length, and is unable to 

 feed through its mouth; and so for about a fortnight it 

 obtains its nutriment solely from the food-yolk contained 

 in the yolk-sac, which hangs down from the lower surface 

 of the body. During this period it is active and leads a 

 surface life, partly swimming spasmodically by contrac- 

 tions of the muscular tail, and partly drifting passively 

 with the current. It can do little as yet to avoid an 

 enemy, and is easily caught with a small net, a dish, or a 

 dipping tube. After about a fortnight the larva begins 

 to feed. The yolk has then been used up, the jaws have 

 formed, bones have developed in its body, the muscular 

 system is stronger, and the little fish is able to pursue and 

 capture prey, to eat and digest its food. This at first 

 consists of Diatoms, the spores of sea weeds and other 

 vegetable matters, and a little later on of Copepoda and 

 other minute animals. Post-larval stages taken from 

 our pond in May were found when 5 mm. long to be 

 feeding on alga spores, and when 7 mm. on Copepoda. 



The young post-larval plaice, when it begins to feed, 

 is about one month old, counting 18 days for hatching and 

 12 for the absorption of the yolk. Another month is 

 probably required, as a rule, for the transformation of this 

 bilaterally symmetrical little fish into the completely 

 metamorphosed unsymmetrical flat-fish, with both the eyes 

 on one surface (the right side) of the body, and with a 

 distribution of pigment which causes this upper side to be 

 dark-coloured and the lower light. Young plaice, with 

 the metamorphosis completed, have been found only a 

 little over half an inch in length (14 mm.) in June ; but 

 they are usually about an inch long when they appear in 

 our sandy bays during the summer. In the post-larval 

 stages they lived at the surface, so during the period of 

 their transformation they must be making their way to 

 c 



