. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 156 THE DEVELOPMENT OF THE GAMETES OR SEX CELLS HECAL LAYER !— FOLLICLE CELLS ZONA RADIATA •PERIPHERAL MITOCHONDRIAL ZON • - ^^_,VARIOUS STAGES OF -^^J?^ T R AN SFOR M ATION OF '•^MITOCHONDRIA INTO. Fig. 88. Portion of follicle and periphery of oocyte from ovary of the adult bird, showing the mitochondria and their transformation into the M-yolk spheres of Brambell. (After Brambell, '25.) Before considering the various aspects of cytoplasmic diffe
. Comparative embryology of the vertebrates; with 2057 drawings and photos. grouped as 380 illus. Vertebrates -- Embryology; Comparative embryology. 156 THE DEVELOPMENT OF THE GAMETES OR SEX CELLS HECAL LAYER !— FOLLICLE CELLS ZONA RADIATA •PERIPHERAL MITOCHONDRIAL ZON • - ^^_,VARIOUS STAGES OF -^^J?^ T R AN SFOR M ATION OF '•^MITOCHONDRIA INTO. Fig. 88. Portion of follicle and periphery of oocyte from ovary of the adult bird, showing the mitochondria and their transformation into the M-yolk spheres of Brambell. (After Brambell, '25.) Before considering the various aspects of cytoplasmic differentiation of the oocyte, it is best for us to review the types of vertebrate and other chordate eggs in order to be able to visualize the various goals toward which the developing oocyte must proceed. 1) Types of Chordate Eggs. Eggs may be classified according to the amount of deutoplasm (yolk, etc.) present in the cytoplasm as follows: a) HoMOLECiTHAL (IsoLECiTHAL) Eggs. Truc homolccithal eggs in the phylum Chordata are found only in the mammals, exclusive of the Proto- theria. Here the deutoplasm is small in amount, and is present chiefly in the form of fat droplets and small yolk spherules, distributed in the cytoplasm of the egg (figs. 118A, B; 147A). b) Telolfcithal Eggs. In the telolecithal egg the yolk is present in con- siderable amounts and concentrated at one pole. Telolecithality of the egg in the phylum Chordata exists in various degrees. We shall arrange them in sequence starting with slight and ending with very marked telolecithality as follows: (1) Amphioxus and Styela. In Amphioxus and Styela from the subphyla Cephalochordata and Urochordata, respectively, the yolk present is centrally located in the egg before fertilization but becomes concen- trated at one pole at the time of the first cleavage where it is con- tained for the most part within the future entoderm cells (figs. 132D, 167A). (2) In many Amphibia, such as the frogs and toads, and also in t
Size: 2367px × 1056px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionameri, bookcollectionbiodiversity
