92 



the Laboratory from an egg artificially fertilised on March 1, 1889. The length 

 of the larva was 2"87 mm. The development of chromatophores in the median 

 fin fold does not take place in this species at so early a stage as in P. flesus. 



Fig. 3 of the same Plate represents a stage in the development of P. microcephalus, 

 the merry sole of the Plymouth fishermen, the lemon sole of Scotland and most parts 

 of England. The larva from which this figure was drawn was also hatched in the 

 Laboratory, and was four days old ; a small quantity of yolk still remained in the 

 body cavity. The chromatophores at this stage form five well-marked interrupted 

 transverse bands. 



Fig. 4 of the same Plate represents a larva of the plaice {P. pi atessn), just after the 

 complete absorption of the yolk. This larva was also hatched in confinement : it was 

 drawn on February 27, five days after hatching. The larva of the plaice is much 

 larger than that of any of the other species here mentioned : at the stage figured it was 

 6'5 mm. in length. 



Fig. 5 represents the appearance and natural size of a living larva of the brill 

 {Rhombus Icevis). The young of the turbot and brill remain pelagic until after the 

 completion of the metamorphosis, that is, they swim about near the surface of the 

 water, ai\d are commonly met with in the still waters of inlets and liarbours at the 

 proper time of year, namely, in June and July. The one here represented was taken 

 in Sutton Pool, Plymouth, on June 1. Their pelagic habit is correlated with the 

 development of a relatively large air bladder, an organ which is entirely wanting 

 in the adult. Although they swim freely in the surface waters they do not swim 

 vertically when the right eye has migrated to the left side, but horizontally ; during 

 metamorphosis their inclination from the vertical in swimming is proportional to the 

 degree of asymmetry of their eyes. 



II 



