. The cell in development and inheritance. Cells. I go FERTIUZATIOX OF THE OVCM while in Cluctof^tcnis and Picris the first ]-»olar spindle has advanced into the anaphase.' It is an interesting and signiHcant fact that the aster or amphiaster always leads the way in the march toward the egg-nucleus ; and in many cases it ma\- he far in advance of the sperm-nucleus.^ Boveri {^'^'J, i) has observed in sea-urchins that the sjierm-nucleus may indeed be left entirely behind, the aster alone conjugating with the egg-. Fig. 96.— Diagrams of two principal types of fertilization. /. Polar bodies formed
. The cell in development and inheritance. Cells. I go FERTIUZATIOX OF THE OVCM while in Cluctof^tcnis and Picris the first ]-»olar spindle has advanced into the anaphase.' It is an interesting and signiHcant fact that the aster or amphiaster always leads the way in the march toward the egg-nucleus ; and in many cases it ma\- he far in advance of the sperm-nucleus.^ Boveri {^'^'J, i) has observed in sea-urchins that the sjierm-nucleus may indeed be left entirely behind, the aster alone conjugating with the egg-. Fig. 96.— Diagrams of two principal types of fertilization. /. Polar bodies formed after the entrance of the spermatozoa (annelids, mollusks, flat-worms). //. Polar bodies formed before entrance (echinoderms). A. Sperm-nucleus and centrosome at cT ; first polar body forming at 9. B. Polar bodies formed; approach of the nuclei. C. Union of the nuclei. D. Approach of the nuclei. E. Union of the nuclei. F. Cleavage-nucleus. nucleus and causing division of the egg witJiout union of the gcnn- nuclei, though the sperm-nucleus afterward conjugates with one of the nuclei of the two-cell stage. This process, known as " partial fer- tilization," is undoubtedly to be regarded as abnormal. It affords, however, a beautiful illustration of the view that it is the centro- some alone that incites division of the egg, and is therefo7r the fer- tilizing element pi'oper (Boveri, '87, 2). The foregoing facts lead us to a consideration of Boveri's theory of fertilization, which has for several years formed a central point of discussion. The ground for this theory had been prepared by Oscar 1 Cf. p. 181. ^ Cf. Kostanecki and Wicrzejski, ' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wilson, Edmund B. (Edmund Beecher), 1856-1939. New York Macmillan
Size: 1854px × 1348px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
