. Outlines of zoology. Zoology. MATURATION OF THE OVUM. 59 complementary, but the spermatozoon has a longer history behind it. The homologue of the ovum is the mother sperm cell or spermatogonium. This segments much as the ovum does, but the cells into which it divides have little coherence. They go apart, and become spermatozoa. There is a striking resemblance between the different ways in which a mother sperm cell divides and the various kinds of segmen- tation in ova. In most cases the spermatogonium divides into spermatocytes, which usually divide again into spermatides or young spermatozo
. Outlines of zoology. Zoology. MATURATION OF THE OVUM. 59 complementary, but the spermatozoon has a longer history behind it. The homologue of the ovum is the mother sperm cell or spermatogonium. This segments much as the ovum does, but the cells into which it divides have little coherence. They go apart, and become spermatozoa. There is a striking resemblance between the different ways in which a mother sperm cell divides and the various kinds of segmen- tation in ova. In most cases the spermatogonium divides into spermatocytes, which usually divide again into spermatides or young spermatozoa. Maturation of the Ovum.—When the egg cell attains its definite size or limit of growth, it bursts from the ovary or. C D Y\G. 9.—Diagram of maturation and fertilisation. (From " Evolution of ;) A. Primitive sex cell, supposed to be amcKboid. B. Ovum; C of first polar body ('.); £>. formation of second polar body (2. pb.). Bi. Mother sperm cell; Ci. the same divided (sperm-morula or polyplast, or spermatogonium). Vi. Ball of immature spermatozoa or spermatides ; s/. liberated spermatozoa. E. Processor fertilisation ; F. approach of male and nuclei within the ovum. from its place of formation, and in favourable conditions meets either within or outside the body with a spermatozoon from another animal. Before this union between ovum and spermatozoon is effected, generally indeed before it has begun, the nucleus or germinal vesicle of the ovum moves to the periphery and divides twice. This division results in the /ormation and extrusion of two minute cells or polar. 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 Thomson, J. Arthur (John Arthur), 1861-1933; Newbigin, Marion I. (Marion Isabel), 1869-1934; Smith, Preserved, 1880-1941. fmo. New York, D. Appleton &
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