EXPLANATION OF THE PLATES. 53 



Tigs. 11, 1-'. Two examples of the sixteen-c II stage, in one of which a wavy line separates the four central 



cells from i in- i welve marginal ones. 

 Fig 13. A stauc ol' from thirty-two to sixty-four cells. 



Fig. 1 1. A similar stage, showing manj of the marginal cells in a slate of division. 

 Fig 15. A slight]) older stage 



I ! L6. Same, seen from lie' side 



Fig. L7. A still more advanced stage of cleavage. 



1'e.' L8. The blastodisc is split up into very small cells, with a wreath of periblastic nuclei around it. 



Fig. 1'.). An earbj stage of the embryonic ring. 



Fig. 20. Profile view of the disc at the time the ring begins to form. 



21. The axial plal I appears at on.' p .int. of the ring. 

 I' g 22. The ling has now attained ils lull width, and the embryonic plate is much larger. 

 Fig. 23. Embryonic plate still longer, and the ring advanced to an equatorial position. 

 Fig. 21. The embryonic plate seen from above, just after the ring has passed the equator of the egg. Chorda 



broad behind, the boundary lines vanishing before reaching the caudal lobe. 

 Fig. 25. Embryonic ring well advanced ; optic vesicles forming. 



Fig. -21'}. Profile view just after the closing of the blastopore. Kupll'er's vesicle still prominent. 

 Fig. 27. The caudal end already well formed; black pigment-dots appear in two Literal lines. 

 Fig. 28. A later stage, showing a comparatively thick embryo, with somewhat larger pigment-dots. 

 Fig 29. \ still more advanced embryo. 



Fig. -'50. Just before hatching. Yolk-sac already considerably reduced in size, 

 be,' 31. Embryo seen from above at the time of hatching. Pigment extends to end of tail, but only two 



dots seen on the head. 

 Figs. 32 and 33. Two views of the same embryo, some hours after hatching; the chromatophores have 



assumed the dendritic form, and arc much more prominent than in Fig. 31. 

 Fig. 31. A profile view of a young lish about twenty-four hours old. The embryonic fold is remarkably 



narrow on the anterior part of the body. 



PLATES X. an-i> XI. 

 Tautoga onitis, Fin. (T. americana, Stoher.) 



Fig. 1. The egg shortly aft a- tic closing of the blastopore Frj'.n a batch of eggs artificially fertil- 

 ized. X 55. 

 Fig. 1 a. Middle portiou of another embryo of the same stage, showin » fewer pigment-dots. 



2 and :!. Similar portions of different embryos more highly magnified, to show the character of the 

 pigment. X 130. 

 Fiir. 1. Profile view at time of hatching. X 55. 

 Fig, 5. \ portion of Fig I more highly magnified. X L30 



Fig. 6. Frontal view of Fig. f. 



Fig. 7. Frontal view twenty-four hours after hatching. Pigment-cells expanded. X55. 

 Figs s and 'J. Profile and frontal views of a specimen one to two days old. 



Fig. Kb Two days old. Snout more pointed (ban in preceding stage, embryonic fold narrower. Same as 

 Fig 2, PI. VI . in J gassiz's "Youug Stages," etc. (11. Flounders). 



I II. = Agassi/.'s Fig 3 of the same Plate. Snout slill more prolonged; tail shows a tendency to 



heterocercalitj . 



Fig 12. = Agassi/.'s Fig i of the same Plate. Somewhat older stage. Body greatly increased in width, 

 air-bladder prominent, tail re decidedly heterocereal 



PLATES XTI. and XIII. 

 Specie3 Nos. 1, 2, 15. 



Fig. 1. Tin- egg just after the closing of the blastopore'. X 55. 

 Fig. 2. Eighteen hours later. Chromatophores very large. X55. 



