8 THE PELAGIC STAGES OE YOUNG FISHES. 



the posterior margins of the optic vesicles. The yellow pigment is densest 

 along the two sides of the embryo ; and between these two lines, on the 

 dorsal surface, only a lew chromatophores are to be seen, and these are all 

 black. At the end of another hour we find the pigment-cells more numer- 

 ous, and two or three yellow cells are now to be seen on the optic vesicles. 

 The black pigment-dots are smaller than the yellow ones, and mainly con- 

 liucd to the dorsal surface of the embryo. The yellow pigment-dots are 

 both larger and darker than in the preceding stage.-, appearing bright 

 yellow by reflected light, and brownish yellow or orange by transmitted 

 light. At the time of closure of the blastopore, from three to four hours 

 after the first appearance of pigment, the brownish yellow chromatophores 

 are still larger (.(105 to .008 mm.), and have crowded into the constrictions 

 which separate the optic vesicles from the brain. A few of these cells are 

 now seen among the black cells on the dorsal surface. Soon after this 

 stage pigment-cells are found scattered over the entire surface of the 

 yolk (Figs. 1 and 3). 



At the time of hatching (see Agassiz. he. cit., PI. III. figs. 2, 3) there are 

 generally two large patches of brownish yellow along the margin of the dor- 

 sal fold, and four along the ventral. The outer edge of the pectorals is col- 

 ored in the same manner. Two varieties are seen (in Figs. 4 and 5). which 

 differ so widely from the typical form described by Agassiz as to raise the 

 question whether they do not represent a second, and perhaps a third species. 



The specimen represented in Fig. 4 was hatched from an egg measuring 

 only .85 mm., and having 2-3 oil-globules. Another egg of nearly the same 

 size (.82 nun.) was obtained at the same time, and this had only 8 oil- 

 globules. The bright orange pigment-cells were very numerous on the 

 dorsal and ventral folds, as well as the body, except at the caudal end, where 

 only a single black cell was seen. Some black dots were scattered over the 

 middle third of the body and on the yolk-sac alongside the embryo. The 

 surface of the embryo was very rough or granular. 



In Fig. 5 three patches of pigment are seen on the embryonic fold. The 

 chromatophores of the body are still in a state of contraction. They are 

 much less numerous, and their distribution much more even, than in Fig. 4. 

 This specimen was hatched from an egg measuring 1.10 nun. in diameter, 

 and having a very opaque zona radiata, which presented a blotched appear- 

 ance when examined under a magnifying power of a lew hundred diameters. 

 The dimensions of Fig. 1 are as follows: — 



