EMBRYOLOGY AND LARVAL DEVELOPMENT OF TELEOSTEAN FISHES. 99 



In young fish lo mm. in length (fig. 15) the dorsal, anal, and caudal fins are becom- 

 ing well differentiated. The distribution of pigment remains essentially as in the early 

 stages. However, the number of chromatophores, as well as the quantity of pigment, 

 has materially increased. 



As development advances the young fish gradually assume adult characters. Young 

 fish 30 mm. in length (fig. 16) exhibit nearly all the diagnostic characters of the species. 

 The depth of the body in proportion to its length is rapidly increasing and the back is 

 becoming strongly arched. The ground color of the body at this stage is greenish. The 

 black chromatophores have become aggregated to form heavily pigmented areas, which 

 are roughly arranged in transverse bands and give the body the transversely banded 

 appearance characteristic of the adult. 



TAUTOGOLABRUS ADSPERSUS (Walbaum). GUNNER. 



Spawning. — This species spawns in June and July. The majority of the fish taken 

 after July i were spent. However, eggs were abundant in the plankton until July 15 

 and were taken in small numbers as late as August 15. 



Eggs. — ^The eggs are transparent, spherical in form, and 0.75 to 0.85 mm. in diameter. 

 They contain no oil globules and can be distinguished from the eggs of Tautoga onitis only 

 by a slight difference in size, the latter having a diameter of 0.9 to i mm. 



Embryology. — The embryological development of the eggs of this species is typical 

 of pelagic teleostean eggs. It conforms in all essential details to the course of devel- 

 opment as outlined for the eggs of Tautoga onitis and will not, therefore, be discussed in 

 detail. Early and advanced stages of cleavage are illustrated in figures 1 8 to 2 1 . Figure 

 22 illustrates an egg in which the embryonic axis is becoming well differentiated. 



Pigmentation is first observed in embryos which show 10 to 15 somites. The earliest 

 chromatophores appear as minute black dots distributed over the dorsal aspect of the 

 body. The extra-embryonic blastoderm remains free from pigment. The distribution 

 of chromatophores during the early stages is essentially the same as in embryos of 

 Tautoga onitis, and the blastoderm does not undergo any material change until after 

 hatching. However, in the latter species the chromatophores are more numerous and 

 somewhat larger. 



Larval development. — Incubation at laboratory temperature occupied approximately 

 40 hours. The newly hatched larvae (fig. 24) are 2 to 2.2 mm. in length. The yolk sac 

 remains relatively large, and the head is slightly deflected. The vent is located some 

 distance from the posterior margin of the yolk sac and a little more than half the length 

 of the body from the anterior end. The depth of either dorsal or ventral fin fold is 

 greater than the depth of the body posterior to the vent. The chromatophores remain 

 small and are limited almost entirely to the dorsal and dorsolateral aspects of the body. 

 The posterior caudal region and the fin folds remain free from pigment. 



Soon after hatching the distribution of pigment undergoes a marked change. The 

 chromatophores gradually become aggregated into compact masses, as illustrated 

 in figure 25, in a larval fish less than one day after hatching. These masses of chroma- 

 tophores become aggregated still further to form a heavily pigmented area in the dorsal 

 region of the abdominal cavity, another just over the vent, and a third on the ventral 

 aspect of the body approximately halfway from the vent to the tip of the tail. These 

 pigmented areas are illustrated in figure 26 in a larval fish three days after hatching. 



