. The cell in development and inheritance. Cells; Cells. ORIGIN AND GROWTH OF THE GERM-CELLS 109 temperature, females; while those of Mrs. Treat on lepidoptera and of Yung on amphibia seem to leave no doubt that the differentiation here depends on the character of the nutrition, highly-fed individuals producing a great preponderance of females, while those that are underfed give rise to a preponderance of males. These and a multi- tude of related observations by many botanists and zoologists render it certain that sex as such is not inherited. What is inherited is, in Busing's words, only the
. The cell in development and inheritance. Cells; Cells. ORIGIN AND GROWTH OF THE GERM-CELLS 109 temperature, females; while those of Mrs. Treat on lepidoptera and of Yung on amphibia seem to leave no doubt that the differentiation here depends on the character of the nutrition, highly-fed individuals producing a great preponderance of females, while those that are underfed give rise to a preponderance of males. These and a multi- tude of related observations by many botanists and zoologists render it certain that sex as such is not inherited. What is inherited is, in Busing's words, only the particular manner in which one or the other sex comes to development. The detcnninatioii of sex is not by in- heritance, but by the combined effect of external ^ In some of the rotifers, however, sex is predetermined from the begin-. Fig. 54. — Germ-cells in the hydro-medusa, Hydractbiia. [BUNTING.] A. Section through young medusa-bud, with very young ova {ov.) lying in the entoderm; B. Mature gonophore, showing two ova lying between ectoderm and entoderm. ning, the eggs being of two sizes, of which the larger produce females; the smaller, males. In the greater number of cases, the primordial germ-cells arise in a germinal epithelium which, in the coelenterates (Fig. 54), may be a part of either the ectoderm or entoderm, and, in the higher types, is a modified region of the peritoneal epithelium lining the body-cavity. In such cases the primordial germ-cells may be scarcely distinguish- able at first from the somatic cells of the epithelium. But in other cases the germ-cells may be traced much farther back in the develop- ment, and they or their progenitors may sometimes be identified in the gastrula or blastula stage, or even in the early cleavage-stages. Thus in the worm Sagitta, Hertwig has traced the germ-cells back to 1 See DUsing, '84; Geddes, Sex, in Encyclopedia Britannica ; Geddes and Thompson, The Evolution of Sex; Wa'ase, On the Phenomena of Sex-diffe7'
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