The relative susceptibility to x-rays of the eggs and sperm of Arbacia.

Abstract

The eggs and sperm of the sea urchin, Arbacia punctulata, were exposed simultaneously to the same x-rayed treatment and subsequently the x-rayed eggs were fertilized by untreated sperm, and untreated eggs were fertilized by x-rayed sperm. Untreated eggs and sperm from the same sea urchins were used in the control cultures. Two sets of experiments have been completed, one during the summer of 1923 and the other during the summer of 1924. In 1924 the conditions of the x-ray treatment were so arranged that the temperature of the water in which the eggs or sperm were kept during treatment did not vary from that of the room in which all the cultures were kept by more than 1° C. The temperature of the room during the different experiments varied from 19° to 22° C. The x-ray treatment was given with a standard Coolidge tube, tungsten target, at 50,000 volts and 3 milliamperes, the distance from the target to the eggs and sperm being 25 cm. In 1923 a portable radiator type tube with tungsten target was used and run at 50,000 volts and 2.5 milliamperes. The distance from the target to the germ cells was 11 cm. and the glass cups were surrounded by a lead box covered on the top where the x-rays entered by a thin sheet of aluminum 3 mills in thickness.

After the treatment of the eggs and sperm, fertilization was brought about in finger bowls and the larvae were reared up to forty-eight hours after fertilization, at which time samples were fixed in 2 per cent formaldehyde. In these samples where development had proceeded at the normal rate in the controls it was found that a considerable number of the pleutei were in a stage where the larger arms were appreciably longer than the rest of the body. This stage was numbered six and the development previous to this was divided into five stages as follows: 1, blastula; 2, gastrula; 3, gastrula which has become triangular and shows the beginnings of the two larger arms; 4, these two arms have developed but are appreciably shorter than the rest of the body; 5, the arms are approximately the same length as the rest of the body. In the case of each sample the stage in development of one hundred larvae was recorded.