University of California Publications in Physiology Volume 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ...with thirty minutes' exposure, many more will segment in the next lot, with thirty-five minutes' exposure. Here also the number of normally segmenting eggs is larger than the number of abnormally segmenting eggs, but only a fraction of the total number of eggs segment. The next lot, with forty minutes' exposure, will suddenly show a decided change. The majority, if not all, of the eggs segment, but the proportion of normally segmenting eggs is smaller than in the previous lot; as a rule about half of the eggs go into a normal two-cell stage, and the segmentation begins in this lot as a rule a little earlier than in the two previous lots. In the subsequent lots the number of eggs which segment decreases gradually although slowly, but the proportion of eggs which go into a normal two-cell stage decreases rapidly. Of the eggs which were exposed for an hour or more to the hypertonic sea-water none, or at least but few, begin their development with a normal two-cell stage. I have gathered the impression that the character of the first segmentation forecasts the relative number of normal embryos which will rise to the surface of the sea-water, and develop into normal plutei. The proportion of normal larvae in a lot of eggs seems to run parallel with the proportion of eggs which from the first show a normal segmentation, and I am inclined to believe that these eggs give most, if not all, the normal larvae which are obtained by this method. When the temperature is lower, and occasionally at a temperature of 20 C. the first lot of eggs to show segmentation is one with a slightly longer exposure to hypertonic sea-water than thirty minutes. In this case everything remains as stated above, except the time of exposure. It may require as much as 45 or 50 minutes' exposur...