EFFECT OF X-RADIATION ON CUMINGIA EGGS. 211 



much larger than the AB cell (Morris). The CD cell divides 

 before the AB producing a 3-cell stage, then a 4-cell. After the 

 third division cleavage becomes irregular, the D cell, or its deriva- 

 tives, remaining for some time distinctly larger than the other 

 blastomeres. 



EXPERIMENTS. 



In the set of experiments here recorded, all exposures to the 

 X-ray tube were made at the same time; thus all three-minute 

 irradiations were under the tube simultaneously All three- 

 minute irradiations were removed at the same time, as were all 

 fifteen-minute irradiations. Consequently there is in all the data 

 presented no question whatever as to any varying amount of 

 exposure for the same length of irradiations. 



The irradiation intensity was therefore, a constant; hence, 

 we may neglect it entirely and take the time in minutes as a 

 measure of the amount of irradiation, not concerning ourselves 

 quantitatively with the physical units involved. This is a much 

 simpler method since when one attempts to calculate the amount 

 of irradiation he enters a field entirely beyond the scope of this 

 paper. What we wish to show is the comparative effect of 

 different amounts of irradiation when conditions are identical. 



Heat, the dilution of the suspension, and the other external 

 factors were kept constant in order to neglect them and reduce 

 any possible chance for error by a faulty technique or varying 

 conditions. 



Four series of experiments were set up. In the A series the 

 eggs were irradiated immediately after fertilization; in the B 

 series, sperm were radiated and then used to fertilize normal eggs; 

 in the C series, eggs were radiated and then fertilized by normal 

 sperm; in the D series, both egg and sperm were radiated before 

 fertilization. 



The first experiment was carried on to test the effect of short 

 and long irradiations on the freshly fertilized egg. For this test 

 fresh sperm and eggs were obtained from the individual animals 

 and immediately mixed. Fertilization took place immediately. 

 This lot was divided into three parts, one for control and two 

 for experiment. All were allowed to develop under similar con- 

 ditions. Samples of the three lots were fixed at intervals during 



