Abstract
ABSTRACT The jelly capsule of amphibian eggs is an impediment to O2 diffusion to the embryo. This effect can be evaluated with a diffusion equation that relates the rate of O2 uptake (Vo2), Krogh's coefficient of diffusion in jelly (Ko2), the geometry of the capsule which is characterized by its inner and outer radii (r. and ro), and the O2 partial pressure difference across the capsule (ΔPo2). Data for Ko2 are presented to enable calculation of the O2 conductance (Go2) of the capsule from its dimensions. As Vo2 increases during embryonic development, Go2 also increases by swelling of the capsule due to osmotic absorption of water into the perivitelline space; thus, changes in ΔPo2 are minimized. The changes in Go2 appear inexorably linked to the embryonic stage, and cannot be modified during development to adapt to high O2 demand or low ambient Po2. ΔPo2 is very sensitive to changes in ri, but less sensitive to ro. Consequently, failure to absorb enough water into the perivitelline space can result in se...
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