Text-book of comparative anatomy . PIG. 25.—Ovarian egg cell of a , Formative yolk ; kb, germinalvesicle; i/W, white yolk; yd, yellow yolk ;dh, yolk membrane. (After O. Hertwig.) 30 COMPARATIVE ANATOMY CHAP. 1. An outer yolk membrane, secreted by the yolk itself. 2. The formative yolk, a small whitish mass in which lies the germinal vesicleat one pole of the egg, viz. the animal pole. 3. The yellow nutritive yolk, which represents the principal mass of the egg,and which appears in concentric layers. 4. The white nutritive yolk, which forms a thin outer layer round the yellowyolk benea
Text-book of comparative anatomy . PIG. 25.—Ovarian egg cell of a , Formative yolk ; kb, germinalvesicle; i/W, white yolk; yd, yellow yolk ;dh, yolk membrane. (After O. Hertwig.) 30 COMPARATIVE ANATOMY CHAP. 1. An outer yolk membrane, secreted by the yolk itself. 2. The formative yolk, a small whitish mass in which lies the germinal vesicleat one pole of the egg, viz. the animal pole. 3. The yellow nutritive yolk, which represents the principal mass of the egg,and which appears in concentric layers. 4. The white nutritive yolk, which forms a thin outer layer round the yellowyolk beneath the yolk integument and the formative yolk, and which also sinks intothe middle of the yellow yolk from the animal pole in the form of a thick strand witha swollen rounded end. When the egg thus formed passes out of the ovary into the oviduct, the walls ofthe latter secrete around it the last envelopes, which are : 1. The albumen with the chalaza, somewhat denser spirally twisted. Fir,. 26.—Diagrammatic longitudinal section of a newly-laid Hens egg, after Allen Thomsonand O. Hertwig. Formative yolk ; white yolk; yellow yolk ; w. albumen ; ; air-chamber ; , inner ; outer layer of the shell membrane ; s. shell, yolkmembrane ; x. a somewhat fluid layer of albumen surrounding the yolk. strands of albumen, which go from the yolk membrane out towards the two ends ofthe egg. 2. The double shell integument, which surrounds the albumen on all two membranes which form this integument separate, and between them a cavityfilled with air arises at the blunt end of the egg—the air chamber. 3. The porous calcareous shell. These three parts, therefore, represent theaccessory integuments of the egg. Male Reproductive Cells, or Spermatozoa (Fig. 27). These belong to the smallest cells formed in the animal body. Eachspermatozoon is a simple cell, as is shown by its development which isgenerally complicated, and
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
