The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . the Monera, isa conception which in the present condition of histologicalknowledge seems quite allowable; for we can even yetdirectly observe this oldest histological process of differ-entiation in Ontogeny. It will be remembered that in the THE MONERULA. 51 egg-cell of animals, either before or after fertilization, theoriginal kernel disappeared. We explained this phenomenonas a reversion or atavism, and assumed that the egg-cell,in accordance with the law of latent heredity, first fallsback
The evolution of man : a popular exposition of the principal points of human ontogeny and phylogeny . the Monera, isa conception which in the present condition of histologicalknowledge seems quite allowable; for we can even yetdirectly observe this oldest histological process of differ-entiation in Ontogeny. It will be remembered that in the THE MONERULA. 51 egg-cell of animals, either before or after fertilization, theoriginal kernel disappeared. We explained this phenomenonas a reversion or atavism, and assumed that the egg-cell,in accordance with the law of latent heredity, first fallsback into the kernel-less, cytod stage (Fig. 165). It is onlyafter fertilization is accomplished that a new cell-kernelarises in this cytod, which thus becomes the parent-cell(Cytula, Fig. 166). The transitory kernel-less cytod-con-dition, intermediate between the egg-cell and the parent-cell, is an interesting germ-form, because, in accordancewith the fundamental law of Biogeny, it reproduces theoriginal, oldest parent-form of the Moneron; we thereforecall it the Monerula. (Cf. vol. i. pp. 178-183.). Fig. 165.—Monerula of Mammal (Rabbit). The fertilized egg-cell afterthe loss of the nucleus is a simple ball of protoplasm {d). The outer coveringof the latter is formed by the modified zona pellucida (z) together witha mucous layer (h) secreted on to the outside of the latter. In this a fewsperm-cells are still visible (s). Fig. 166.—Parent-cell (Cytula) of a Mammal (Rabbit): 7r, parent,kernel; n, nucleolus of the latter; p, protoplasm of the parent-cell; z,modined zona pellucida ; s, sperm-cells ; h, outer albuminous covering. 52 THE EVOLUTION OF MAN. We have already explained the one-celled germ-form,which we see in the original egg-cell and the parent-cellwhich is originated by the fertilization of the egg-cell, asthe reproduction of a one-celled parent-form, to which weascribed the organization of an Amoeba (cf. Chap. VI.). Forthe Amoeba, as it yet lives widely distributed in
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