. An atlas of the fertilization and karyokinesis of the ovum. Ovum; Fertilization (Biology); Meiosis; Embryology -- Echinodermata. ENTRANCE OF THE SPERMATOZOON ETC. 15 shown, extending from the base of the sperm-nucleus outwards to the periphery, where the entrance-cone appears (not quite in focus). The centre of the sperm-aster, which may now be called the centrosphere or centrosome appears as a finely granular mass (see Text-fig. X. A and B), lying at the apex of the funnel and evidently derived from the middle-piece. The rays proceeding from it run out at their tips into rows of granules in
. An atlas of the fertilization and karyokinesis of the ovum. Ovum; Fertilization (Biology); Meiosis; Embryology -- Echinodermata. ENTRANCE OF THE SPERMATOZOON ETC. 15 shown, extending from the base of the sperm-nucleus outwards to the periphery, where the entrance-cone appears (not quite in focus). The centre of the sperm-aster, which may now be called the centrosphere or centrosome appears as a finely granular mass (see Text-fig. X. A and B), lying at the apex of the funnel and evidently derived from the middle-piece. The rays proceeding from it run out at their tips into rows of granules indistin- guishable from the microsomes of the general reticulum, with which they are perfectly continuous. These is reason to believe, as explained beyond, that the astral rays do not properly grow forth from the central mass, as they seem to do, but arise through a radial rearrangement of the pre-existing reticulum under the influence of the centrosome to which they converge. -â¢â¢â cT'T^'N'/.'-. â¢^\I^.,â ^â¢^ â â ~4"" y-< B Fig. X. Fig. X. â Structure and growth of the sperm-aster; 4000 diameters. A Very early stage (i^ minutes). The middle-piece (now the centrosome) forms a distinct rounded body lying at the base of the sperm-nucleus. A number of short astral ravs are forming about it. They may be traceil out at their tips directly into the general reticulum. B. Later stage (3 minutes). The sperm-head has moved further inwards, its rays are more numerous and extend further out into the cytoplasm. .\s the figure shows, the rays arise by the direct transformation of the reticulum. In some cases the central mass of the sperm-aster is described as containing an extremely minute deeply staining bod)', which has been regarded as representing the true centrosome at this stage (see p. 20). Such a body cannot be seen in Toxopneustcs, and the evidence indicates that the entire central mass (, the substance of the original middle-piece) is here the centros
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Keywords: ., bookauthorwilsoned, bookcentury1800, bookdecade1890, bookyear1895
