TATJTOGA ONITIS. 23 



form. The vent is marginal, at some distance behind the yolk-sac, and a 

 little behind the middle. Round white refractive bodies (nuclei?) are faintly 

 seen over the entire surface. 



Dimensions at the time of hatching: — 



Length 3.05 mm. 



Yolk-sac 1.00 X -48 " 



Yolk-sac to vent .......... .55 " 



Vent to tip 1.10 " 



Width of head 35 " 



Width, of body at bind end of yolk-sac ...... .15 " 



Dimensions at twenty-four hours old : — 



Length 3.25 mm. 



Yolk-sac 85 X =45 " 



In the course of the first twenty-four hours after hatching, the ehroma- 

 tophores begin to expand, assuming a dendritic form. In this expanded 

 state of the pigment the young fish appears quite dark (Figs. 7-10), and is 

 easily seen if placed on a white ground. It requires only a lv\v moments, 

 however, to change the pigment from the expanded to the contracted form, 

 when the fish again becomes as transparent as it was at the time of hatching. 

 During the second day the yolk-sac becomes much reduced in size, the 

 pectorals double their length, and the eye. already granular in its external 

 half at twenty-four hours (Fig. 7), now shows a little green pigment. 



Figs. 8-10 were all hatched from eggs fished up by surface skimming, 

 and show the form and appearance of the pigment in somewhat different 

 states of expansion. The wreath of cells seen on the head in these figures 

 disappears in the later stages, leaving only a single large branched chroma- 

 tophore on the snout (Figs. 11, 12). The remaining stages were taken with 

 the surface net, and consequently wo can state nothing definite in regard to 

 their age; but their identity with this species is plainly shown by the char- 

 acter and distribution of the black pigment, and especially by the blue-green 

 color of the eyes. The pale brownish-yellow appears first on the head and 

 fore part of the body (Fig. 11), and becomes coextensive with the black 

 pigment in the latest stage here figured (Fig. 12). The principal changes 

 to be noted in these stages are the prolongation of the jaws, the tendency to 

 heterocercality in the tail, and the increased width of the body. 



