MOTELLA AEGENTEA. 41 



In the course of the next twenty-lour hours ( Fig. 4 is about four days 

 old) the chromatophores become more crowded with pigment-granules, while 

 retaining the general shape, size, and distribution seen in the previous stage. 

 They are pretty evenly sprinkled over the whole free surface of the embryo, 

 but when seen from the ventral side they appear to form two dense lateral 

 streaks of stellate or dendritic cells. A rich network of liner-branched lead- 

 gray chromatophores surrounds the oil-globule. By this time a few pigment- 

 cells may be seen on the inner or ventral surface of the embryo, and only 

 two remain on the yolk-sac. In another egg, at a like stage of develop- 

 ment, no pigment was found on the yolk, and the chromatophores exhibited 

 a dendritic form only on the tail and oil-globule, elsewhere having a rounded 

 or angular form, varying in size from .008 to .015 mm. Eighteen horns 

 later the pigment had not advanced beyond the stage of development seen in 

 Fig. 4, although the embryo was much longer, the tail nearly reaching the 

 head. 



The next stage (Fig. 5 is about five days old) represents the embryo 

 about twelve hours before hatching. The tail now overlaps the head, and 

 the median fin-folds are well developed. The pectorals are also well 

 advanced. The localization of pigment is already in progress, which in 

 the course of another twenty-four hours is to end in the peculiar pat- 

 tern seen in Fig. 0. The posterior half of the eyes is thickly dotted 

 with black. A few large dendritic cells are seen on the head, a much 

 larger number along the alimentary tract, another cluster at the middle 

 of the tail, and a single spot near the end of the tail on the ventral side 

 of the muscular axis. The concentration in these different regions only 

 becomes more pronounced in the next stage, representing thje same em- 

 bryo twelve hours after hatching (Fig. 6). The whole eye is now jet- 

 black, with a reflection of green in some parts. The alimentary canal is 

 sheathed in a dense layer of black chromatophores; a broad black patch 

 is located midway between the vent and the tail, a much smaller spot is 

 seen near the tip, and a paler patch just above the hind end of the 

 alimentary tube. Three or four less conspicuous spots are seen on the 

 head, and two small pigment cells close to the otic capsule. Elsewhere 

 the young fish is pure transparent white. The oil-globule is still covered 

 with pigment, and much reduced in size. The vent is at the hind end of 

 the yolk-sac, high up on the ventral fold. The following measurements 

 were taken from this stage : — 



