. The cell; outlines of general anatomy and physiology. ecomes either suddenly or gradually split upinto as many daughter-cells as there are nuclei in it. Free cell-formation occurs chiefly, in both plants and animals,during the development of the sexual products. In order todemonstrate it, I will select three examples: the superficialsegmentation of the centrolecithal eggs of Arthropoda, the for-mation of the endosperm in the embryo-sac within the ovule ofPhanerogamia, and the formation of spores in the sporangia ofSaprolegnia. The yolk mass is generally collected in the centre of the eggin A
. The cell; outlines of general anatomy and physiology. ecomes either suddenly or gradually split upinto as many daughter-cells as there are nuclei in it. Free cell-formation occurs chiefly, in both plants and animals,during the development of the sexual products. In order todemonstrate it, I will select three examples: the superficialsegmentation of the centrolecithal eggs of Arthropoda, the for-mation of the endosperm in the embryo-sac within the ovule ofPhanerogamia, and the formation of spores in the sporangia ofSaprolegnia. The yolk mass is generally collected in the centre of the eggin Arthropoda, being surrounded by a thin peripheral layer ofprotoplasm. Hence the eggs are called centrolecithal, eggswith yolk in the centre, in distinction to telolecithal eggs, in whichthe yolk is situated at the poles (Balfour VI. 3). The cleavagenucleus, surrounded by a protoplasmic envelope, is generally inthe centre of the nutritive yolk ; here it divides into two daughter-nuclei, whilst the division of the egg itself does not immediately B C.
Size: 1249px × 2002px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookidcelloutlines, bookyear1895
