205 
Pigmentation of the 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 sae) 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 cesophagus 
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 
