. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RECIPROCAL AXDROCFXFTIC FROG HYBRIDS 89 lected in the breeding season with the eggs in the oviducts. Sperm were obtained by cutting up the testes in a small quantity of spring water. Approximately 20 minutes after fertilization the eggs were examined to see if the region where the second polar body comes off was visible. This region, which is called the "Keimpunkt" or "Eispek" by the German authors, is a very small, round, dark indentation on the surface of the animal pole and marks the position of the se
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RECIPROCAL AXDROCFXFTIC FROG HYBRIDS 89 lected in the breeding season with the eggs in the oviducts. Sperm were obtained by cutting up the testes in a small quantity of spring water. Approximately 20 minutes after fertilization the eggs were examined to see if the region where the second polar body comes off was visible. This region, which is called the "Keimpunkt" or "Eispek" by the German authors, is a very small, round, dark indentation on the surface of the animal pole and marks the position of the second maturation division spindle (Fig. 1). Using the method of Porter (1939), the maternal chromosomes were removed by inserting the tip of a sturdy glass needle under the Eispek and lifting the second maturation division spindle out in a small exovate. The eggs subsequently cleaved with only the paternal chromosomes. This method of removal of the maternal chromosomes is successful 97 per cent of the time. The removal of a small exovate does not injure the egg nor alter its later development. This was tested by removing a small amount of protoplasm a short distance from the Eispek. Xo effect on subsequent development was noted. At the early blastula stage the androgenetic embryos, marked by the small exovate, were separated from the diploid embryos. Only blastulae in which the operation. FIGURE 1. The egg of Rana palitstris 20 minutes after fertilization, showing the small, dark Eispek at the animal pole. had been well performed were maintained. Approximately equal numbers of diploid blastulae were kept as controls. The embryos were raised in a 12° C. cold room. The embryos were fixed in Smith's fluid, sectioned at 10 micra, stained with the "Xuclealfarbung" method of Feulgen, and counterstained with light green (Moore and Ryan, 1940). The sectioned embryos were studied and chromosomal counts made. To check on the interpretations, certain embryos were restainol with
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
