Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 Fig. 101.—0\ im of N'ophelis (ifter O Ucrtwir^). a, tlie ovum half-an-hour after deposition. a projecti juot tlie protoplasm iiidic ites the commencing f jrmation of the first polar body ; the nuclca. „p.„Jl \....Lle. I, TL., same an hour later, with polar body extruded, and after entrance of the spermatozoon. Sh, male pronucleus, e. The same another hour later without egg membrane, and with two polar bodies and male pronucleus (Si-); d
Elementary text-book of zoology, general Elementary text-book of zoology, general part and special part: protozoa to insecta elementarytextbo00clau Year: 1892 Fig. 101.—0\ im of N'ophelis (ifter O Ucrtwir^). a, tlie ovum half-an-hour after deposition. a projecti juot tlie protoplasm iiidic ites the commencing f jrmation of the first polar body ; the nuclca. „p.„Jl \....Lle. I, TL., same an hour later, with polar body extruded, and after entrance of the spermatozoon. Sh, male pronucleus, e. The same another hour later without egg membrane, and with two polar bodies and male pronucleus (Si-); d, the same an. hour later with approximated female and male pronuclei; i^i', polar bodies. DEVELOPMENT. It follows from the facts of sexual reproduction that the simple cell must be regarded as the starting-point for the development of the organism. The contents of the ovum sponbineously or under the influence of fertilization enter upon a series of changes, the final result of Avhich is the rudiment of the body of the embryo. These changes consist essentially in a process of cell division which implicates the whole protoplasm of the ovum, and is known as segmentation.
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