MARINE BIOLOGICAL STATION AT PORT ERIN. 139 



and if it were possible to so regulate matters, it would be 

 very desirable, in the interests of the fisheries, that each 

 mature plaice should be allowed to spawn at least once 

 before being caught. The spawning in our seas takes 

 place in the early months of the year — a little earlier or 

 a little later, according to the locality and temperature of 

 the season — but we may say, in general, from January or 

 February to May, with a maximum in March. The 

 fertilised egg is spherical and transparent, floats at the 

 surface of the sea, and measures about l-12th of 

 an inch (1*9 mm.) in diameter. The period that the 

 embryo remains inside the egg-covering also depends, to 

 some extent, upon the temperature of the sea water at the 

 time. It may probably vary from a fortnight to three 

 weeks; and seventeen or eighteen days may be taken as 

 an average time. During the last fortnight of this period 

 the young fish may be clearly seen with the microscope 

 inside the egg-covering (see accompanying figures), and 

 for the last few days before hatching it lies coiled up, and 

 occasionally moving, ready to burst through its shell and 

 emerge as a larva (fig. XXXIII.). 



When the larval plaice hatches out (see fig. XXXIV.) 

 it 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 contractions 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 



