. Bulletin of the United States Fish Commission. Fisheries -- United States; Fish-culture -- United States. J>P BAIRDIELLA CHRYSURA. Fig. 9.—Egg showing later stage in differentia- tion of embryonic shield; qt, gerro ring; es, embryonic shield. Fig. 10.—Egg showing embryonic shield (ci) with embrj'onic area (fa) outlined; tea, extra-embry- onic area; gr, germ ring; pp, posterior pole of blastoderm. outlined it is somewhat broader in the anterior or head region than in the posterior region. Observed in surface view (fig. 10) the embryonic area now has a more or less regular spatulate form. W
. Bulletin of the United States Fish Commission. Fisheries -- United States; Fish-culture -- United States. J>P BAIRDIELLA CHRYSURA. Fig. 9.—Egg showing later stage in differentia- tion of embryonic shield; qt, gerro ring; es, embryonic shield. Fig. 10.—Egg showing embryonic shield (ci) with embrj'onic area (fa) outlined; tea, extra-embry- onic area; gr, germ ring; pp, posterior pole of blastoderm. outlined it is somewhat broader in the anterior or head region than in the posterior region. Observed in surface view (fig. 10) the embryonic area now has a more or less regular spatulate form. While the embryonic shield is growing forward into the subgerminal cavity and the embryonic axis is becoming differentiated, the germ ring is continually advancing around the yolk sphere. By the time the embryonic axis becomes well differentiated the blastoderm covers more than three-fourths of the surface of the yolk (fig- II)- The further differentiation of the embryo ad- vances very rapidly and the germ ring continues to advance round the yolk until the blastoderm covers the entire surface of the yolk sphere and the blas- topore is completely closed. In the eggs observed while the germ ring was advancing round the yolk sphere the posterior pole of the blastoderm main- tained approximately the same position with respect to the oil globule. Inasmuch as the oil globule main- tains a more or less constant position with respect to the early blastoderm, it is obvious that the posterior pole of the blastoderm remains at a relatively fixed point. This Wilson (1889) observed to be the case also in the eggs of Serranus atrarius. In the eggs under observation the closure of the blastopore occurred before i o'clock a. m. This is probably not more than six hours after fertilization. At the time of the closure of the blastopore the embryo extends about halfway round the circumference of the yolk sphere. There is as yet no evidence of pigmentation in either the egg or the growing embryo
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Keywords: ., bookcentury1900, bookcollectionbiod, bookdecade1910, bookyear1913
