22 THE PELAGIC STAGES OE YOUNG FISHES. 



The eggs of Ctenolabrus, Ps. melanogaster, and Tautoga all agree in having no 



globule ; and their difference in size is not sufficiently great and constant 

 to serve always as a safe guide to identification. The close resemblance of 

 these eggs and their simultaneous occurrence make it very difficult, if not 

 impossible, to distinguish them when promiscuously mixed, as they usually 

 are when taken by surface skimming. Up to the time of hatching, and for 

 some time afterward, the color, distribution, form, and number of chroma- 

 tophores are so much alike in the three species that few distinctive marks 

 can be named. At the time of hatching, Ctenolabrus has little or no pig- 

 ment on the head, and may thus be distinguished from the Tautog, in 

 which there is a continuous line of pigment encircling the front and sides 

 of the head. Another but less striking difference is the extension of the 

 pigment-dots farther backward in Ctenolabrus than in the Tautog, as will 

 lie seen by comparing Fig. 4 with Fig. 31 of Plate IX. The same distinc- 

 tions hold between Ctenolabrus and Ps. melanogaster, if our identifications 

 of the latter are correct. The Tautog is considerably larger and propor- 

 tionally longer than the dinner, as shown in the two figures just referred to. 

 The eggs of the Tautog are most abundant in the early part of July, but 

 they are also found in June and August. The eggs of Ctenolabrus occur in 

 greatest abundance from the middle of May to the middle of June. The 

 average size of these eggs is .88 to .89 mm., while those of the Tautog vary 

 between .90 and .95 mm. 



At the time the blastopore closes there is not a trace of pigment in 

 any part of the Tautog egg. Soon after the tail has assumed the blunt 

 rounded form and begun to lengthen backward (Fig. 1), minute black pig- 

 ment-dots appear over the whole dorsal surface of the embryo. Different 

 eggs vary considerably in the number of pigment-dots (Figs. 1-3). When 

 seen from above, the dots often appear to be arranged in two lateral lines, 

 one on each side of the chorda (Fig. 3). The dots are nearly round, and jet- 

 black, and the largest are not more than .005 mm. in diameter. 



In the newly hatched embryo (Fig. 4, sixty-six hours after fertilization) 

 the dots have increased in size (.007 to .015 mm.), while remaining about the 

 same in number. The longitudinal growth of the embryo has increased 

 the distance between adjoining dots, and left the tail free from pigment. The 

 continuity of the two lines of pigment around the head, which is character- 

 istic of this and a number of the following stages, is well shown in Fig. 6. 

 The yolk-sac which is entirely free from pigment, has an ovate-elliptical 



