46 THE PELAGIC STAGES OF YOUNG FISHES. 



rounded or angular, and thickest just behind the eyes and along the lateral 

 surfaces. The black pigment-cells are of about the same size, usually angular, 

 much fewer in number, and mainly confined to the median dorsal surface. 

 On the inner surface of each globule are seen a considerable number of com- 

 paratively large, gray, amoeboid cells, and on the outer surface a somewhat 

 larger number of brownish yellow cells precisely like those on the embiyo. 



Eighteen hours later (Fig. 2), the pigment shows a much less uniform 

 distribution, becoming concentrated into four regions. The black pigment 

 of the body is now represented by a very few cells, and the gray pigment- 

 cells of the inner surface of the globule have become yellow, and are only 

 about twice the size of those on the outer surface. A large median space 

 in the region of the otic capsules is without pigment. 



The next stage (Fig. 3) is only a few hours older, but it represents 

 another egg, in which the pigment-cells are somewhat larger and more 

 deeply colored. The globule is now completely invested with pigment. 

 The color is here a dirty sienna. This species bears a close resemblance 

 to Hemitripterus in the color and density of its pigment, but is easily dis- 

 tinguished by the complete absence of pigment on the yolk-sac and by its 

 large globule. 



At the time of hatching, the concentration of the pigment in four re- 

 gions is usually much better marked than would appear from Fig. 4. which 

 is exceptional in not having any well-defined pigment region on the head 

 and trunk. In another individual of the same stage the pigment-cells are 

 mostly round and sharply defined, and distributed in a head region, a trunk 

 region a little behind the otic capsules, an intestinal region at the posterior 

 end of the yolk-sac, and a caudal region midway between the marginal vent 

 and the tip. In Fig. 4 the chromatophores are in a state of expansion, 

 etivine a more diffuse colorina:, which obscures the distinction between the 

 head and trunk regions. In the individual above referred to there was no 

 pigment on the yolk-sac, and only a few inconspicuous black cells scattered 

 along the dorsal line of the middle third of the fish. This specimen was 

 rather short, and the dorsal fold arched but little. The measurements of 

 this stage are as follows : — 



Total length ' 2.10 mm. 



Yolk-sac 75X.50 " 



Yolk-sac to vent . .10 



Vent to tip 1-10 " 



Width of head . .32 " 



Width of body at vent 15 " 



