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New PDF release: Animal Species for Developmental Studies: Vertebrates

By T. A. Dettlaff (auth.), T. A. Dettlaff, S. G. Vassetzky (eds.)

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The head is bent sideways. If the envelopes are removed, the tail is completely straightened (33); the fin fold continues to widen. Stage 34. Tail end reaches diencephalon (Fig. 13). The embryo moves actively within the envelopes. If the envelopes are removed, the embryo is capable of slow progressive movement. The fin fold is markedly widened. Stage 35. Onset of hatching (Figs. 14). The tail end reaches the pronephros, but only if the envelopes remain un stretched. Prior to hatching, however, the envelopes are often markedly stretched and the embryo within is somewhat straightened; in such cases the position of the tail end cannot serve as a diagnostic feature of the stage.

The envelopes surrounding the egg are swollen and their layers become discernible. The jelly coat becomes sticky. The egg rotates inside its envelopes and becomes oriented with the animal pole upward. Stage 3. Light crescent stage (Fig. 7). The displacement of the superficial cytoplasm layer is complete; the pigment accumulation which was in the center of the animal region at stage 2 becomes displaced. At the margin of the animal region a light, sometimes white, crescentlike area is often seen.

The male is stunned, and spermatozoa stripped into a dry vessel. Spermatozoa can be taken 2-3 times from the same male. When necessary, the males can be used for 3-4 days. The volume of a single ejaculate is 25-500 cm3• Eggs and spermatozoa for experimental purposes are collected at the time when they are obtained at the hatcheries for breeding. The eggs are taken in dry wide test tubes (30-35 mm wide, with flat bottoms) up to half the height of the tube and with a layer of body-cavity fluid on top.

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