TAUTOGA ONITIS. 21 



this sheet of cells remains, the whole of it having been incorporated in the 

 body of the embryo. 



As in the Tautog, no trace of pigment appears in the egg until some 

 time after the closing of the blastopore. They are first seen as minute black 

 dots (.003 mm. in diameter) scattered along the middle third of the dorsal 

 surface of the embryo. By the time the stage of Fig. 27 is reached, the 

 dots are larger and somewhat more numerous, and extend in two more or 

 less irregular lateral lines along nearly the whole length of the embryo, 

 being absent only on the fore part of the head and the tip of the tail. 

 From this stage to the time of hatching (Figs. 28-31), the pigment-cells in- 

 crease somewhat in size, while remaining about the same in number. They 

 still preserve the round form in the stage of Fig. 31, the larger ones meas- 

 uring .01 mm. in diameter; and, roughly speaking, they appear to form two 

 lateral lines when seen from above. In profile views, the dots are seen to 

 be confined to the dorsal half of the body, precisely as in the case of the 

 young Tautog. The embryo of this stage differs, however, from the Tautog 

 and Ps. melanogaster in having no wreath of pigment around the head, and 

 in the extension of the pigment to the very end of the muscular axis. 



Measurements at the time of hatching : — 



Length 2.30 mm. 



Yolk-sa 1.00X.G5 " 



Yolk-sac to vent .......... -25 



Vent to tip 1-05 " 



Width of head 25 " 



The time required for hatching varies from two to six days; and this 

 difference of four days corresponds to a difference in temperature of 8° C. 



For a description of the later stages, see Agassiz, Young Stages, etc. 

 (Part III. pp. 290-294, Plates XI1I.-XV.). 



Tautoga onitis, Lin. (T. americana, Storer.) 



Plates X. and XI. Figs. 1-12. 



During the summer of 1884 experiments were made in artificial fertiliza- 

 tion of the eggs of the Tautog, and in two instances with success. The early 

 stages thus obtained form a very complete series, and they make it certain 

 that Figs. 1-3, and probably Fig. 4, in Plate VI. of Agassiz's Young Stages 

 (II. Flounders), belong to this species, and not to Pseudorhombus melanogaster. 



