. Analysis of development. Embryology; Embryology. 102 Cellular Structure and Activity spindle is commonly proportional to the vol- ume of the nvicleus from which it originates. This is especially clear during cleavage of many organisms (Conklin, '12) where nu- clei and spindles are large in early divisions and get smaller in late ones. In Pediculopsis the spindle volume decreases from the first to the tenth cleavage about 200 fold (Cooper, '39). Other good illustrations are the large and small spermatocjrtes of Arvelius (Schra- der, '47). Where more than one nucleus is present within a cell,
. Analysis of development. Embryology; Embryology. 102 Cellular Structure and Activity spindle is commonly proportional to the vol- ume of the nvicleus from which it originates. This is especially clear during cleavage of many organisms (Conklin, '12) where nu- clei and spindles are large in early divisions and get smaller in late ones. In Pediculopsis the spindle volume decreases from the first to the tenth cleavage about 200 fold (Cooper, '39). Other good illustrations are the large and small spermatocjrtes of Arvelius (Schra- der, '47). Where more than one nucleus is present within a cell, each forms its own spindle. During early cleavage sperm and to all spindles is the bipolar organization. This bipolarity is independent of centriole and aster as demonstrated by the cases where centrioles are naturally inactive (for in- stance in oogenesis of Ascaris) or experi- mentally inhibited (Bataillon and Tchou Su, '30). In the living cell the spindle is a gelatin- ous semi-solid body that can be moved about in the cell or even dissected out with the micromanipulator (Chambers, '24; Carlson, '52). Cytoplasmic granules never penetrate the spindle (which differentiates the true. Fig. 17. The birefringence of the spindle. A, Pollen mother cell of Liliwn lonpiflorum (phot. Inoue). B, Amphiaster and spindle isolated from the blastomere of a sea urchin (phot. Inoue. see Mazia and Dan, '52). egg chromosomes often remain separate and each group forms its own spindle (gonom- ery). Such independent spindles may fuse into one or remain separate through ana- phase (Hughes-Schrader, '24). The spindle may become organized inside the nuclear membrane or only after the membrane has dissolved. In some cells the membrane does not disappear until anaphase or even persists throughout mitosis (intranuclear spindles; cf. Drosophila cleavage. Fig. 14). The form of the spindle is very variable; it may be shaped like a disc, a barrel or a spindle, or may be flared at either end, or it may be asy
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