4 THE PELAGIC STAGES OF YOUNG FISHES. 



figs. 8, 10, PI. XII. figs. 0, 7, PL XIII. figs. 10, 11, PI. XIV. figs. 6, 7, PI. XVI. 

 figs. 6, 7, PL XVII. fig. 6. PL XVIII. figs. 6-9, PL XIX. figs. 4-6.) 



The speed of the resorption of the yolk mass varies also greatly, as can 

 be readily seen while comparing the young embryos of the stages indicated 

 above. The rapidity of development of the structural features of the young 

 fish is correlated with the decrease of the size of the yolk-bag. We find in 

 those young fishes, for instance, in which the yolk-mass retains for many 

 days an inordinate size, that the development of the head, the fins, the eyes, 

 and the pigment-spots has been comparatively slow. 



It is rather an unusual thing to find the chromatophores dendritic in the 

 earlier stages within the egg, although in a few species in which the pigment 

 is principally black this seems to be the case. (PI. II. fig. 2, PL XIII. fig. 3, 

 PL XVII. fig. 1, PI. XVIII. figs. 4, 5.) 



Soon after hatching, however, the development of the dendritic pigments 

 is very marked ; the black pigments are usually the first to be extended, and 

 the colored chromatophores appear in later stages, except in those species (as 

 in some of the Cottoids) in which the colored chromatophores form the basis 

 of the ornamentation even in the earliest stages. The arrangement of the 

 patterns of coloration is also blocked out soon after hatching, during the 

 earliest stages of growth. (PL II fig. 12, PL III. figs. 9-11, PL V., PL XIII. 

 fig. 15, PL XV.) 



The eyes are generally colorless until some time after the hatching of 

 the embryo, but in some species the chromatophores extend over the eye 

 (PL II. figs. 0, 7), and in others (PL II. fig. 2, PL XII. fig. 3, PL XVIII. fig. 5) 

 there is an accumulation of black granules in the posterior part of the eye 

 while still within the egg. Ordinarily the eye does not become pigmented 

 black till after hatching, and the coloring is not developed until somewhat 

 later stages. (PL XL fig. 11, PL XIII. figs. 14, 15, PL XV., PL XVI. figs. 8, 

 10, PL XVIII. fig. 10, PL XIX. fig. 7.) 



The fust tins formed are the pectorals, traces of which appear in very 

 early stages within the egg (PL XII. fig. 1, PL XIV. fig. 2, PL XVI. fig. 2. 

 PL XVIII. fig. 2) as slight swellings in the sides of the body of the embryo. 

 The closing of the blastopore and the disappearance of Kupffer's vesicle are 

 followed by the growth of the tail (PL II. fig. 4, PL X. fig. 1, PI. XII. fig. 1) 

 and the formation of an embryonic tail-fin, which increases in width with the 

 increase in size of the posterior part of the body (PL II. figs. 6, 8, PL XII. 

 figs. 2, 3, PL XIV. figs. 3-5, PI. XVI. figs. 3. 4. PL XVIII. figs. 3-5, PL XIX. 



