EMBRYOLOGY AND LARVAL DEVELOPMENT OF TELEOSTEAN FISHES. II5 



Eggs were first taken in the tow in Muskeget Channel on July 30. They were 

 present in the plankton off Gay Head throughout August, being especially abundant 

 on August 20. Larval fish 2 to 3.2 mm. in length were taken at this point on August 

 12 and again on August 16. On August 7 a young butterfish 6 mm. in length and on 

 August 14 another 7.5 mm. in length were taken in Woods Hole Harbor. Eggs or newly 

 hatched larvae were never taken in the harbor. These larger young fish show many 

 of the diagnostic characters of the species and can be positively identified. Although 

 young fish between 3.2 and 6 mm. in length were not taken, it is believed that the eggs 

 and smaller larval fishes here described are this species. 



The authors have since learned that at the Gloucester, Mass., fisheries station, 

 from July 15 to 31, inclusive, 609,000 eggs were secured and somewhat over 60 percent 

 hatched. This is believed to be the first successful attempt at taking the eggs from 

 the parent fish. 



Eggs. — ^The eggs are transparent, spherical in form, and 0.7 to 0.8 mm. in diameter. 

 The yolk sphere usually contains a single transparent oil globule 0.17 to 0.20 mm. in 

 diameter. Eggs with two oil globules of smaller size are not uncommon, but as develop- 

 ment advances these coalesce. The egg membrane is thin and homy. 



Embryology. — These eggs develop in a manner typical for pelagic teleostean eggs. 



An advanced cleavage stage is illustrated in figure 58. Figure 59 illustrates an advanced 



stage in the differentiation of the embryonic axis. Figure 60 illustrates an egg shortly 



after the closure of the blastopore. At this time the embryo extends approximately 



' halfway around the circumference of the yolk sphere. 



As soon as the embryo is well differentiated, black chromatophores appear sparsely 

 scattered over its entire surface as well as in the extra-embryonic blastoderm and on 

 the oil globule. As the time of hatching approaches (fig. 61) these chromatophores 

 become relatively large. 



Larval development. — Incubation occupies less than 48 hours. The newly hatched 

 larvae (fig. 62) are approximately 2 mm. in length. The head is slightly deflected at 

 the anterior end of the yolk sac. The vent is located just posterior to the yolk sac, 

 not at the margin, but laterally,' considerably above the margin of the fin fold. Large 

 black chromatophores are sparsely scattered over the body and the oil globule. A 

 small group of chromatophores also remains in the posterior region of the yolk sac. 



Soon after hatching, a small amount of yellow pigment becomes apparent. Small 

 yellow areas appear on the head and the dorsal surface of the body, another at the vent, 

 and a few on the oil globule. The black chromatophores, as illustrated in figure 63, in 

 a larval fish one day after hatching, gradually become aggregated into small groups. 

 By the close of the third day after hatching (fig. 64) these groups of chromatophores 

 have become aggregated still further to form a heavily pigmented area on the nape, 

 another in the dorsal region of the abdominal cavity, a third on the ventral surface of 

 the body less than half the distance from the vent to the tip of the tail, and a fourth 

 directly opposite the third on the dorsal surface of the body. At this time the yolk is 

 completely absorbed and the larvae are approximately 2.3 mm. in length. The larval 

 fishes kept in sea water died before the close of the fourth day. 



In yoimg fish 3.2 mm. in length (fig. 65) the head is relatively large and the anterior 

 region of the trunk relatively deep. The distribution of pigment remains essentially 

 as in the preceding stage. 



