. Journal of morphology. the most advanced ovocytes. X 300. Letter-ing as in the preceding figures. The ovocyte in the advanced growth stage is thus surroundedby a single-layered follicle, suspended in a flask-shaped two-layered sac of which the inner layer is the cyst membrane, theouter layer is the inner epithelial membrane of the ovarian a broader sense, the entire three-layered structure may becalled a follicle, and the neck of the flask-shaped sac may be calledthe stalk of the follicle. This triple-layered wall persists withoutany radical change in structure up to the time of matu
. Journal of morphology. the most advanced ovocytes. X 300. Letter-ing as in the preceding figures. The ovocyte in the advanced growth stage is thus surroundedby a single-layered follicle, suspended in a flask-shaped two-layered sac of which the inner layer is the cyst membrane, theouter layer is the inner epithelial membrane of the ovarian a broader sense, the entire three-layered structure may becalled a follicle, and the neck of the flask-shaped sac may be calledthe stalk of the follicle. This triple-layered wall persists withoutany radical change in structure up to the time of maturation. EMBRYOLOGY OF CRYPTOBRANCHUS 111 In the later stages of the development of the ovary, its wallsanastomose by the formation of cross-walls or partitions, divid-ing the ovary into compartments or perhaps pockets; by thesecross-walls the course of the inner ovarian membrane is greatlycomplicated. The ovocyte of a female of 26 cm. and younger is apparentlya naked cell, possessing no proper membrane. In females with a. Fig. 18 Cross-section through the ovarian wall of a 26 cm. Cryptobranchusallegheniensis, showing one of the most advanced ovocytes. X 180. n., nucleolus;v., vitelline body; ep., inner epithelial membrane of the ovarian wall. Otherlettering as in figs. 13 to IG. body length of from 30 to 35 cm. there occurs a rapid developmentof two non-cellular membranes closely investing the egg withinthe follicle. The inner of these two membranes exhibits a radialstriation and is the zona radiata; at the time of maturation itbecomes a simple cell wall to the egg. The outer membrane,clear and homogeneous, is the zona pellucida; it persists as thevitelline membrane of the embryo. 112 BERTRAM G. SMITH The zona radiata and the zona pellucida begin to form simul-taneously, shortly before the appearance of yolk granules. Inthe most advanced ovocytes of a 35 cm. female, these membranesare well established and a narrow zone of yolk has appeared nearthe periphery of the ovocyte (see
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