A text-book of dental histology and embryology, including laboratory directions . Diagram showing stages of spermatogenesis as seen in different sections of aseminiferous tubule of a rat: s, Sertoli cell; sc1, spermatocyte of the first order;sc2, spermatocyte of the second order; sg, spermatogone; sp, spermatid; sz, sperma-tozoon. (Von Lenhosseks diagram, from McMurrich.) the male pronucleus, the other the female pronucleus. Theseboth form chromosomes, the number from each being halfthe number typical of the species. These are arranged asusual between the centrosomes. They divide longitudinall
A text-book of dental histology and embryology, including laboratory directions . Diagram showing stages of spermatogenesis as seen in different sections of aseminiferous tubule of a rat: s, Sertoli cell; sc1, spermatocyte of the first order;sc2, spermatocyte of the second order; sg, spermatogone; sp, spermatid; sz, sperma-tozoon. (Von Lenhosseks diagram, from McMurrich.) the male pronucleus, the other the female pronucleus. Theseboth form chromosomes, the number from each being halfthe number typical of the species. These are arranged asusual between the centrosomes. They divide longitudinally,each forming two, one of which passes to either centrosome,where a new nucleus is formed, and in the meantime thecytoplasm has divided so that two cells are formed. Thenuclear material of these two cells has, therefore, beenequally derived from the two parents, and it is to controlall of the future development of the individual. Fig. 261. HOLOBLASTIC SEGMENTATION 345 SEGMENTATION Holoblastic Segmentation.—An idea of the development ofthe embryo can perhaps best be obtained by following thedevelopment of the frog. The frogs eggs are large andeasily observed, and they contain only a small amount ofyolk or food material, which does not obstruct the observa-tion. The spherical ovum first divides into hemispheres; these
Size: 1297px × 1926px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectteeth, bookyear1912
