205 



Pigmentation of tlie embryo begins on the 9th day by 

 the formation of a row of yellow branching chromato- 

 phores on either side of the body ; on succeeding days 

 these become very abundant and extend on to the head 

 and cover uniformly the trunk and tail. Black pigment 

 appears on the 13th day as a row of round chromatophores 

 on each side of the body. Later on these become abun- 

 dant and of a branching form. On the 14th day the eye 

 becomes pigmented, and has a greenish-golden sheen. 



The little fish hatches out from the egg on the 17th 

 day. It (fig. 35) is about 6'5mm. in total length — a rela- 

 tively large size among newly hatched Pleuronectids. The 

 yolk sac is very large. A continuous broad fin runs along 

 dorsal and ventral margins of the body and round the tail. 

 The notochord is straight at the tip, and only rudiments 

 of the pectoral fins are present. It is covered (except the 

 yolk sac) with bright canary-yellow chromatophores, and 

 branching black chromatophores are situated along either 

 side of the body. The eyes are greenish-gold in colour. 

 The mouth is open ; the gut is a nearly straight tube 

 slightly dilated at one part and terminating in the anus 

 at the posterior margin of the yolk sac. The oesophagus 

 is open, but has an exceedingly contracted lumen, and 

 there is an extensive yolk sac circulation. A pronephros 

 as described above also exists. The urocyst is in connec- 

 tion with the hind gut, and does not open directly to the 

 exterior. The young fish is still perfectly symmetrical. 



The larval period and metamorphosis. — The larval 

 period lasts from the time of hatching until the definitive 

 form and asymmetry of the adult has been acquired ; that 

 is till about 6 weeks from hatching. For the first week 

 there is little change in the larva except that during that 

 time the yolk is being gradually absorbed, and at the end 

 of 8 days the yolk sac has disappeared. The larva now 



