. Journal of morphology. f yolk granules. X 340. The strip shownextends about half-way to the germinal vesicle, c, cyst membrane; cy., yolk-free peripheral zone of cytoplasm; ep., inner epithelial membrane of the ovarianwall;/o/., follicular membrane i)ropcr; z. p., zona poUucida; z. r., zona radiata;y. and y., layers of fine and coarse jolk granules respectively. layer of fine yolk particles and an inner layer of coarse yolk par-ticles, separated by a narrow region poor in yolk. In the largest residual eggs (2 to 3 mm. in diameter) of spentfemales, the yolk-laden zone has extended inward furt
. Journal of morphology. f yolk granules. X 340. The strip shownextends about half-way to the germinal vesicle, c, cyst membrane; cy., yolk-free peripheral zone of cytoplasm; ep., inner epithelial membrane of the ovarianwall;/o/., follicular membrane i)ropcr; z. p., zona poUucida; z. r., zona radiata;y. and y., layers of fine and coarse jolk granules respectively. layer of fine yolk particles and an inner layer of coarse yolk par-ticles, separated by a narrow region poor in yolk. In the largest residual eggs (2 to 3 mm. in diameter) of spentfemales, the yolk-laden zone has extended inward further than EMBRYOLOGY OF CRYPTOBRANCHUS 119 outward; a very narrow zone of clear cytoplasm persists at theperiphery, and a much broader zone containing only a few scat-tering yolk granules surrounds the germinal vesicle. The middleportion of the yolk zone is now filled with coarse yolk granules;its margins consist of fine yolk particles. The germinal vesicleis still centrally situated, and the arrangement of yolk zones and. Fig. 23 Meridional section through one of the most advanced ovocytes of anadult Cryptobranchus allegheniensis killed July 6. The bounding line repre-sents the zona radiata. X 20. cytoplasm is concentric. The nucleoli are still distributed at theperiphery of the germinal vesicle, with only a slight tendencytoward concentration at the outer side. In the largest ovocytes of adults killed July 6 (see fig. 23),the germinal vesicle occupies a position midway between thecenter of the egg and the periphery, on the more exposed side ofthe egg, toward the stalk of the follicle. The animal pole is thus 120 BERTRAM G. SMITH defined by a point on the surface, toward which the germinalvesicle is moving. The cytoplasm is now everywhere thicklyinterspersed with yolk granules; these granules are in generalcoarse throughout the central portion of the egg, finer andmore densely packed at the periphery. Axial differentiation inthe arrangement of yolk particles is now for the firs
Size: 1605px × 1556px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1, booksubjectphysiology, bookyear1912
