206 



begiirs to feed. It is probable that it feeds before the 

 yolk has been entirely absorbed. The food is necessarily 

 small, consistino' of diatoms and larval molluscs. It 

 grows very slowly, and at the age of 25 days from batching 

 is only about T'Smm. in total length and about I'Gmm. in 

 height. After this the increase in height is relatively 

 greater than that in length. Larval Crustacea now form 

 the principal food. The tail, wbich has hitherto preserved 

 its embryonic homocercal character, now bends upwards 

 at the tip, and ventral to this upturned portion fin rays 

 begin to be formed (fig. 36). 



Up to 30 days after hatching the larva has retained 

 its bilateral sjanmetry, and at this stage is precisely 

 similar in form to the ordinary symmetrical Teleostean 

 larva. The greater relative growth dorso-ventrally than 

 longitudinally indicates the beginning of the metamor- 

 phosis, and after the 30tli day the left eye begins to move 

 dorsalh' and anteriorly. 40 days after hatching it appears 

 on the dorsal margin of the head just anterior to the right 

 eye. On the 45th day the left eye has attained its defini- 

 tive position on the apparent right side dorsal and anterior 

 to the right eye. The larva is about 13|^mm. long and 

 ()|mm. high. During the period in which the eyes are 

 rotating the young fish gradiially acquires a new j)osition 

 in swimming ; the vertical plane of its body slopes more 

 and more from right to left as the eyes shift round so that 

 in swimming the plane passing through both eyes is 

 always horizontal. At the completion of metamorphosis 

 the whole symmetry of the head has been profoundly dis- 

 turbed, though that of the body remains as before, except 

 that the opening of the ureter has shifted from the median 

 ventral line to the right side. The horizontal swimming 

 plane of the whole body has been rotated through a right- 

 angle and the fish rests and swims on its morphological 



