ON SOME LARVAL STAGES OP FISHES. 71 



choroid membrane. The auditory vesicle is very large^ and extends 

 dorsalwards far above the level of the eyes. The pigmentation of 

 the skin is characterised by the development of very definite spots 

 along the sides of the dorsal and ventral fin membrane. In the 

 centres of these spots as well as over the sides of the body there 

 are small orange spots in addition to the yellow and black of the 

 eai'lier stages. Judging from what I have seen in the skin of the 

 adult plaice and sole, I believe that the orange is not a new pig- 

 ment, but the same pigment as the yellow in a more concentrated 

 form ; in fact I have reason to conclude that there are only two 

 pigmeiits in the skin of flat fishes, the black and the yellow, the 

 latter being yellow when spread out, orange or even red when con- 

 centrated into a thicker globule. It will be seen on comparison 

 that my fig. 3 differs very greatly from the figure of a larval sole 

 of about the same size, 5 mm., given by Professor Mcintosh in 

 Plate III of the seventh Annual Report of the Scottish Fishery 

 Board. We do not know the whole development of the sole with 

 sufficient completeness to justify a definite assertion on the matter, 

 but I cannot help doubting for the present whether Professor 

 Mcintosh's figure represents a stage of the larval sole at all. 



In my paper published in this Journal March, 1889, I was unable 

 to describe the larva of the mackerel. In the summer of that year 

 I succeeded in hatching some artificially fertilized ova of the 

 species, but could not keep them alive for any length of time. 

 Pressure of other work has prevented me since from devoting much 

 attention to the mackerel, and all I have to add now is a figure of 

 the newly hatched larva, fig. 4. The drawing reproduced in this 

 figure was made on July 2nd, 1889. The egg, from which the 

 larva hatched, was one of a number artificially fertilized for me by 

 mackerel fishermen on board their own boats. The length of the 

 larva was 4*23 mm. In structure the larva does not differ essen- 

 tially from other species belonging to the Physoclisti, or Teleosteans 

 with closed air-bladders. 



As in most other larvse of that division, the rectum is immediately 

 behind the short oval anterior yolk-sac. The notochord is as usual 

 multicolumnar, composed of several columns of cells. The mouth 

 is not open, and the eye (choroid membrane) is unpigmented. The 

 slender elongated form of the larva is characteristic. But the chief 

 distinguishing feature is the pigment of the skin and its distribution. 

 The pigment consists of chromatophores of two colours, black and 

 green, as in the adult. There is no pigment at all on the pri- 

 mordial median fin membrane. Black chromatophores occur over 

 the sides of the body and head, especially along the edges of the 

 body. The green chromatophores, mingled with black, occur only 



