122 



BULLETIN OF THE BUREAU OF FISHERIES. 



Pigmentation begins within several hours after the closure of the blastopore. Before 

 the time of hatching (fig. 79) small black chromatophores appear more or less closely 

 aggregated on the dorsal and dorsolateral aspects of the embrvo. The extra-embryonic 

 blastoderm remains free from pigment. 



Larval development. — Incubation occupies not over 48 hours. The newly hatched 

 larvae (fig. 80) are approximately 4.5 mm. in length and relatively slender. The head 

 is slightly deflected at the anterior end of the yolk sac. The vent is located less than 

 one-fifth the length of the body from the posterior end. Pigment is less abundant than 

 before hatching. Small black chromatophores now oCcur on the dorsal aspect of the 



Fig. 85. — Young fish 41 mm, in length. 



Fig. 86— Adult fish. 

 BREVOORTIA TVRANNUS. 



body near the base of the dorsal-fin fold and on the ventral aspect of the body posterior 

 to the vent. 



Four days after hatching (fig. 8i) the larvae have grown to a length of approximately 

 5.7 mm. Pigment is no longer apparent on the dorsal aspect of the body except near 

 the tip of the tail. A small group of chromatophores occurs in the caudal region, also 

 on the ventral aspect of the body. Black chromatophores are now present in a series 

 along the digestive tube from the level of the pectoral fins to the vent. 



In young fish 9 mm. in length the dorsal fin is becoming differentiated. In the 

 posterior abdominal region the intestine is already distinctly convoluted. The distribu- 

 tion of pigment remains essentially as in the preceding stage. 



In young fish 23 mm. in length (fig. 83) all the fins are well differentiated. The 

 body remains relatively slender. Black chromatophores now occur superficially on the 

 nape, along the margin of the opercle, near the base of the dorsal, anal, and caudal fins, 



