. Elements of Comparative Anatomy. GENEEATIVE ORGANS OF ARTHROPODA. 301 o creases tlie laro'est forineJ in these terminal filaments, tlio cell-masses of wliich represent ovarian germs j these, while undergoing continual differentiations, gradually make their way out of the ovarian tube. The ovam is a true cell at the place where it is formed, but on its way through the ovarian tube it in- iu size, so that we find gs farthest from the germinal region, and nearest the oviduct, while behind them there is a continual series of smaller and younger formations up to the above-mentioned blind end of t
. Elements of Comparative Anatomy. GENEEATIVE ORGANS OF ARTHROPODA. 301 o creases tlie laro'est forineJ in these terminal filaments, tlio cell-masses of wliich represent ovarian germs j these, while undergoing continual differentiations, gradually make their way out of the ovarian tube. The ovam is a true cell at the place where it is formed, but on its way through the ovarian tube it in- iu size, so that we find gs farthest from the germinal region, and nearest the oviduct, while behind them there is a continual series of smaller and younger formations up to the above-mentioned blind end of the ovarian tube. The separate eggs cause the ovarian tube to appear to be divided into segments or chambers. The gradual descent of the egg is not only correlated with its growth, but with various changes also in the substance of the yolk; each egg is provided, especially in the last segment of the tube, with an external cuticular investment, the so-called chorion; this is formed by the epithelial layer of the ovarian tube. As each egg passes into the so-called oviduct, a portion of the ovarian tube is degenerated, and so the egg next in front is brought close to the oviduct. The differentiation of the egg is accompanied by the growth of the thin end of the ovarian tube, which is made up for by its shortening at the other end. In. Fig. 158. A Ovarian tube of the Flea. n Ovum, g Germinal vesicle. B Ovarian tube of a Beetle (Carabus violac eus). 0 Ovarian segment, clivifled into two por- tions, of whieli tbe ovarian cell is marked a, and the vitellogenous layer h. The ovum of the last segment has been ex- pelled ; the walls of the ovarian tube are collapsed (after Lubbock). many Insects a group of cells is differentiated with each egg, in addition to the epithelial layer sur- rounding it; this vitellogenous layer occupies the portion [b) of the chamber («) behind the egg-cell (Fig. 158, B a), but is gradually used up by the latter, as it grows. An ovarian tube, or a collec- tion
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