. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. 68 ANIMAL PHYSIOLOGY. protection. The appearance of relative opacity in some of the parts marked off as ahove is to be explained by thickening in the cell-layers of which they are composed. The Origin of the Fowl's Egg.— The ovary of a young but mature hen consists of a mass of connect- ive tissue {stroma), abundantly, supplied with blood-vessels, from which hang the capsules which contain the ova in all stages of development, so that the whole sug
. A text-book of animal physiology, with introductory chapters on general biology and a full treatment of reproduction ... Physiology, Comparative. 68 ANIMAL PHYSIOLOGY. protection. The appearance of relative opacity in some of the parts marked off as ahove is to be explained by thickening in the cell-layers of which they are composed. The Origin of the Fowl's Egg.— The ovary of a young but mature hen consists of a mass of connect- ive tissue {stroma), abundantly, supplied with blood-vessels, from which hang the capsules which contain the ova in all stages of development, so that the whole suggests, but for the color, a bunch of grapes in an early stage. The ovum at first, in this case as in all others, a single cell, becomes com- plex by addition of other cells {dis- cus proligerus, etc.), which go to make up the yelk. All the other parts of the hen's egg are additions made to it, as explained before, in its passage down the oviduct. The original ovum remains as the blas- toderm, the segmentation of which may now be described briefly, its character being obvious from an examination of Fig. 72, which rep- resents a surface view of the seg- menting fertilized ovum {oosperm). A segmentation cavity appears early, and is bounded above by a single layer of epiblast cells and below by a single layer of primi- tive hypoblast cells, which latter is soon composed of several layers, while the segmentation cavity dis- appears. The blastoderm of an unincu- bated but fertilized egg consists of a layer of epiblastic cells, and beneath this a mass of rounded cells, arranged irregularly and ly- ing loosely in the yelk, constitut-. FiG. 71—Female generative organs of the fowl (after Dalton). A, ovary; 5, Graafian follicle, from which the egg has just been discharged ; C, yelk, entering upper extremity of oviduct ; D, E, second portion of oviduct, in which the chalaziferous membrane, chalazae, and albumen are formed ; F^ third portion, in which the fibrous shSll membranes are pro
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Keywords: ., bookauthormillswes, bookcentury1800, bookdecade1880, bookyear1889
