. Journal of experimental zoology. us has^^ now become as large as the originalgerminal vesicle and it lies in the non-spherular protoplasm beneath the ecto-plasmic band. In some cases theFig. 58. Eggs taken from female cctoplasmic defcct at the animal poleat 9 A. M., centrifuged at A. M. bccomcs covetcd up (Fig. 59), and then •Fertilized a. m. Drawn about (.j^jg banded fotm docs not occut; in such p. M., four hours and thirty-five 1 1 • i 1 . f ,.,. cases the ectoplasm snnplv becomes minutes after fertilization. r r > more massed. There are some reasons for thinking that t
. Journal of experimental zoology. us has^^ now become as large as the originalgerminal vesicle and it lies in the non-spherular protoplasm beneath the ecto-plasmic band. In some cases theFig. 58. Eggs taken from female cctoplasmic defcct at the animal poleat 9 A. M., centrifuged at A. M. bccomcs covetcd up (Fig. 59), and then •Fertilized a. m. Drawn about (.j^jg banded fotm docs not occut; in such p. M., four hours and thirty-five 1 1 • i 1 . f ,.,. cases the ectoplasm snnplv becomes minutes after fertilization. r r > more massed. There are some reasons for thinking that the polar masses ofendoplasm are of different composition, thus it will be noticedthat the original lower mass (Photograph L) affects the photo-graphic plate less strongly than the upper mass, though to the eyethey appeared alike in color. The mere separation is also evidence for some difference incomposition, though it is to be admitted that it does not constitutedecisive proof. A third reason is found in the presence in the. Elementary Phenomeyja of Embryonic Development iij lower mass of a small reticular area usually clearly marked at thisstage (Fig. 60) and always absent in the upper mass. These factsare mentioned only as indicating that the original (or earlyinduced) diversity of substances in the endoplasm may be greaterthan one would suppose. The opposed masses in this case corre-spond roughly to the endoplasm of the first generation of ecto-meres (upper mass) and of the other cells (lower mass). Thedistinction is not between endoplasmic substances a and r, forthese occur in each mass. 2. Concerning the Groiuth of the Nucleus.—Nuclear growth isusually accompanied by nuclear division involving the formationand division of a definite number of chromosomes at periodicintervals. Now in the eggs that we are describing the nucleusdoes not divide, but it grows and undergoes periodic changes thatcorrespond to the periodic changes of dividing nuclei. Thusin any preparation
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1904
