258 THE COD FAMILY. 



minute spots of yellow pigment also invading the marginal 

 fin. This early appearance of yellow pigment is a remarkable 

 specific feature of the whiting, and its presence serves as a 

 ready means of distinguishing the embryo from that of a cod 

 or a haddock. 



It is customary amongst the zoologists of to-day to attempt 

 to explain the presence or absence of particular pigments in 

 animals by the influence of natural selection upon variations 

 which may be advantageous in the particular environment of 

 the organism, but it is difficult with our present knowledge to 

 assign any direct advantage to the embryonic whiting by the 

 presence of yellow pigment, which would not apply equally to 

 the cod. It is hardly possible that the later breeding-season 

 and greater proximity to the shore can be, at any rate, direct 

 factors in causing this diversity. 



The larval fish (Plate XI, fig. 1) emerges on the tenth day 

 (in April), and measures 3'2 to 3'5 mm. A noteworthy feature 

 is the pale greenish yellow tinge, due to the fine yellow 

 pigment. The larvae are beautifully translucent and move 

 about actively in the surface-water. 



Plate XI, fig. 2, shows a young whiting at the close of the 

 larval period ; it is the latest stage yet reared in confinement. 

 Besides the diffuse yellow pigment there are double rows 

 of black chromatophores, the outer one in each series being 

 most prominent, that lying dorsally extending to the front of 

 the head and that ventrally becoming very conspicuous over 

 the stomach. The rows come to an abrupt termination before 

 reaching the tail, a frequent character in other species. 

 Scattered masses of black chromatophores on the lower jaw 

 and ventral part of the abdomen complete the coloration. 

 The eye is of a beautiful metallic blue ; the lower jaw pro- 

 trudes beyond the snout and is without the upward angular 

 inflexion which gives so peculiar an aspect to the larval cod. 

 A largo serous cavity is present on the dorsal region in those 

 in confinement. We may note that there is no indication 

 whatever in the larval whiting of the barred or striped appear- 

 ance which is so marked in the little cod, and indications of 

 which are also found in many plouronectids. 



