According to Heymons, the yolk-cells must be Metameric Segmentation.
In eggs which contain a larger quantity of food-yolk, the process by which the endoderm is enveloped by the ectoderm is somewhat different.
(The ovary (a) leads into (bb) the oviduct, which is joined at (g) by the duct of the yolk-glands (h, h, Y).
In diameter, with little yolk, and the embryos provided with large trophic vesicles (Willey).
The shell is thick, and operculate in some forms; thin, and provided with filaments, in others; in the latter cases it may contain only a few yolk-granules suspended in an albumen-like substance.
