HEMITEIPTERUS A.MERICANUS. 11 



from end to end, .and a few chromatophores on the yolk alongside the 

 embryo. 



As in the Cottus embryo, there are two kinds of pigment-cells, — the 

 brownish yellow (lemon-yellow by reflected light) and the black. The 

 yellow cells, which are by far the more numerous, are generally round, and 

 thickest along the sides of the embryo. The black cells are smaller, more 

 or less angular, and mainly confined to the median dorsal surface of the 

 embryo. Both kinds of pigment are seen on the oil-globule; but here the 

 yellow cells are confined to the external half of the globule, while the black 

 cells are restricted to the opposite (inner) hemisphere. 



A little later (Fig. 0) we find the entire yolk covered with the two kinds 

 of pigment-cells, many of which are expanding, as shown by their irregular 

 form and pseudopodial prolongations. This expansion is carried still further 

 in the next stage (Fig. 7, just before hatching), where we find patches of 

 diffuse brownish yellow resulting from the confluence of expanded chro- 

 matophores. 



At the time of hatching (Fig. S) the condition of the pigment on the 

 body and yolk-sac is about the same as in the stage of Fig. 7, with the 

 exception that the yellow pigment stops short some distance in front of 

 the tip. while the minute round black dots may be traced to the very end 

 of the muscular axis. At this time three large pigment patches are found 

 on the embryonic fold, two on the dorsal portion, and one on the ventral, as 

 shown in Figs. 8 and !). These patches are usually elongated in a longitu- 

 dinal direction, and placed about midway between the margin of the fold 

 and its base. They consist mainly of yellow chromatophores, with a few 

 black cells intermingled. A few chromatophores actually contain black pig- 

 ment granules mixed with the yellow. This union of two different pigments 

 in the same cell has been noticed in other cases. The color of the young 

 fish varies much from moment to moment, according to the contraction or 

 expansion of the chromatophores. Cells with a brownish or reddish hue when 

 contracted, often appear bright yellow when distended. There can be but 

 little doubt that, those young fishes which exhibit such rapid and conspicu- 

 ous variations in color have what has been called the ''chromatic function." 

 The protective nature of these color changes, which have been so well de- 

 scribed by Heincke in the case of Gobins Ruthmsparri, is very evident in the 

 young Tautog and Gunner, and still more so in young Flounders.* 



\ U i i/„ Yoim S Stages, Part II. pp. :?, 11, 11-18 ; Emery, R. Acad. d. Linoei, 1882-83 (Blennius). 



