. A manual of zoology. 60 MANUAL OF ZOOLOGY sect. Before the changes begin which lead to the formation of the multicellular Metazoan, another cell, the male cell or sperm, has to unite with the ovum or female cell. Before this takes place, the ovum throws off portions of its substance (Fig. 26,pel) in the form of two little rounded bodies — the polar bodies. This preliminary process is known as the maturation of the ovum. The male cell or sperm is a relatively small cell, usually motile, which penetrates into. Fig. 25.—Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the prot
. A manual of zoology. 60 MANUAL OF ZOOLOGY sect. Before the changes begin which lead to the formation of the multicellular Metazoan, another cell, the male cell or sperm, has to unite with the ovum or female cell. Before this takes place, the ovum throws off portions of its substance (Fig. 26,pel) in the form of two little rounded bodies — the polar bodies. This preliminary process is known as the maturation of the ovum. The male cell or sperm is a relatively small cell, usually motile, which penetrates into. Fig. 25.—Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the protoplasm, containing yolk-granules, the large nucleus (germinal vescicle), with its network of chromatin and a large nucleolus (germinal spot). (From Bal- four's Embryology, after Hertwig.) the ovum, and coalesces with it — the coalescence being what is termed fertilisation or impregnation — and the immediate result being that, instead of separate ovum and sperm, we have a compound body, the oosperm, formed by their union, but not differing at first in any marked degree from the simple ovum, and containing a single nucleus representing both the nucleus of the sperm and that of the ovum. On impregnation follows the process of segmentation of the oosperm. The nucleus first divides into two; then the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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