I30 



BULLETIN OF THE BUREAU OP FISHERIES. 



Young fish 8 mm. in length (fig. 1 1 1) do not differ essentially in their general appear- 

 ance from the young fish 5 days old just described. The distribution of pigment also 

 remains essentially the same. 



In young fish 12 to 15 mm. in length (fig. 112) the distribution of pigment observed 

 in the earlier stages is still apparent ; however, black chromatophores are becoming more 

 abundant on the dorsal aspect of the body. The silvery lateral band characteristic of 

 the species is not yet well differentiated. The dorsal, anal, and caudal fins are well 

 formed, and the young fish are gradually assuming adult characters. 



GASTEROSTEUS ACULEATUS Linnsus. THREE-SPINED STICKLEBACK. 



Spawning. — The spawning season of this species begins in May (Edwards) and con- 

 tinues until late in July. Females ripe for stripping were taken as late as July 24. 

 Males ripe for stripping were not secured. Fertilization was accomplished by macerating 

 the testes of the male in the water into which the eggs were stripped. 



Eggs. — The eggs are demersal and adhere firmly in small clumps. They are some- 

 what irregular in form when stripped from the female, but become spherical as soon as 

 they become water-hardened. If they adhere closely, adjacent surfaces may remain 

 somewhat flattened. They are yellowish in color, semiopaque and have a diameter of 

 1.5 to I.J mm. The egg membrane is thick and apparently smooth, but strongly adhesive, 

 The yolk sphere contains numerous oil globules of unequal size, which are usually aggre- 

 gated more or less closely. Very minute oil globules also occur sparsely scattered over 

 the surface of the yolk sphere (fig. 113). 



Embryology. — The eggs of this species develop typically. The volume of protoplasm 

 in proportion to the volume of yolk is comparatively small ; consequently the blastodisc 

 (fig. 114 bd), as well as the early blastoderm (fig. 115), covers a relatively small area of 

 the surface of the yolk. Early development advances quite rapidly. Within 24 hours 

 after fertilization the embryo is well differentiated and the blastopore is closed (fig. 116). 



Before the close of the third day of incubation the embryo extends nearly around 

 the circumference of the yolk sphere (fig. 117). The head is relatively broad, and the 

 body tapejs gradually toward the posterior end. Circulation may be observed through- 

 out the entire extra-embryonic blastoderm. Small black chromatophores are present 

 on the dorsal surface of the anterior region of the trunk and in the adjacent areas of the 

 extra-embryonic blastoderm. 



As the time of hatching approaches, the embryo grows larger and the yolk becomes 

 materially reduced (fig. 118). A close-meshed network of blood vessels becomes ap- 

 parent over the entire surface of the yolk sphere. Chromatophores have become larger 

 and more numerous. They are now present over the entire dorsal surface of the embryo, 

 in the adjacent areas of the extra-embryonic blastoderm, and in a series along the 

 ventrolateral aspect of the body posterior to the vent. 



Larval development. — Incubation at laboratory temperature occupied approximately 

 six days. The newly hatched larvae (fig. 1 19) are 4.2 to 4.5 mm. in length. The vent is 

 located a short distance posterior to the yolk sac and more than half the length of the 

 body from the anterior end. The general color of the body is yellowish. Diffuse yellow 

 pigment and small yellow chromatophores occur over the entire body. Large black 

 chromatophores are more or less closely aggregated on the dorsal surface of the body, 



