. The Cambridge natural history. Zoology. EGGS 409 eggs are very small, those of the Plaice, which are exceptionally large, varying from 1-65 to 1'95 mm. An egg-cell consists of living protoplasm and a nucleus, a variable quantity of non-living food-yolk, and of certain envelop- ing and protective egg-membranes. The ova of Fishes differ principally in the amount and disposition of the food-yolk, in the Fig. 234.âDifferent types of egg-segmentation in Fishes. A, a typical teloleeitlial egg. Holoblastic and unequal segmentation in Amia (B) and in Lepidosteiis (C). D, the meroblastic segment
. The Cambridge natural history. Zoology. EGGS 409 eggs are very small, those of the Plaice, which are exceptionally large, varying from 1-65 to 1'95 mm. An egg-cell consists of living protoplasm and a nucleus, a variable quantity of non-living food-yolk, and of certain envelop- ing and protective egg-membranes. The ova of Fishes differ principally in the amount and disposition of the food-yolk, in the Fig. 234.âDifferent types of egg-segmentation in Fishes. A, a typical teloleeitlial egg. Holoblastic and unequal segmentation in Amia (B) and in Lepidosteiis (C). D, the meroblastic segmentation of m. Teleost. , Animal pole; , egg - membrane ; â ma, niacromeres ; mi, micromeres ; n, nucleus ; , oil globule ; p, protoplasm ; , vegetative pole; y, yolk. (From Ziegler: A, after Hertwig ; B, after Whit- man and Eycleshymer ; C, after Eycleshymer.) character of the egg-membranes, and in the presence or absence of special perforations in the egg-membranes for the entrance of spermatozoa into the eggs. In the small ova of some of the lower Chordata { Amphioxus), where the very small quantity of food-yolk is uniformly distributed, and its presence affects all parts of the egg alike, the process of segmentation which follows fertilisation results in the transformation of the entire egg into a mass of approximately equal-sized cells or blastomeres (Fig. 82).. 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 Harmer, S. F. (Sidney Frederic), Sir, 1862- ed; Shipley, A. E. (Arthur Everett), Sir, 1861-1927. ed. [London, Macmillan and Co. , Limited; New York, The Macmillan Company
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
