MARINE FOOD FISHES 115 



end of the tail is crinkled in consequence of being pushed 

 through a very small rent in the egg membrane. 



The life history of the plaice has been very thoroughly 

 investigated. In the early spring numbers of male and 

 female plaice crowd together on the spawning ground. 

 Millions of eggs are shed, fertilised, and then rise to float 

 during their incubation. Hatching occurs on the average 

 about the seventeenth day. When first hatched, the 

 little plaice is about one-fifth of an inch in length and 

 floats with its yolk sac uppermost. At the end of eight 

 days the yolk sac has practically disappeared, and the 

 little fish now commences to feed on diatoms. 



At first the growth is very slow, and at the end of a 

 month the larval plaice is considerably less than half an 

 inch in length, and the eyes are still opposite each other. 

 The fish now increases more in depth than in length, 

 and this is the first indication that the transformation 

 of the symmetrical fish is about to commence. 



The head now gradually rotates and the left eye is 

 carried up into a position above the right eye. About 

 the fortieth day after hatching the left eye appears on 

 the brim of the head, and in another five or six days 

 both eyes are in the position which they occupy in the 

 adult. The whole transformation takes about six weeks, 

 and during this time the plaice has gradually been sink- 

 ing to the bottom, and for the last few days lies on its 

 left side. The upper surface or right side now shows 

 considerable pigmentation, while the lower surface or 

 left side is colourless. 



