PROTOZOA AND INVERTEBRATE EGGS 



301 



S. purpuratus and obtained retardation of first cleavage with, at most, a 

 very slight effect on later divisions. Marshak (1949b) reports that sperm 

 exposed to 2537 A ultraviolet delay the first cleavage but have no appre- 

 ciable effect upon the second. He also reports that there is less delay in 

 division if the sperm are irradiated shortly before insemination than if 

 they are irradiated ^-1^ hr before. Perhaps this increase of the effect 

 with time between irradiation and insemination was due to some sub- 

 stance produced in the medium. 



Blum and Price (1950) report a detailed study of recovery in Arbacia 

 eggs irradiated with ultraviolet from a mercury arc. In most cases, the 



80- 



60- 



\. 



40- 



20- 



NORMAL CLEAVAGE INTERVAL 

 i 



— r— 

 50 



— I — 

 100 



— 1 



150 







(6) 



NORMAL CLEAVAGE INTERVAL 



L 



— 1 — 



50 



100 150 



TIME (MIN) FROM IRRADIATION TO CLEAVAGE 



0,« I st TO 2nd CLEAVAGE 



A,A2ndT0 3rd cleavage 

 □ .■3rdT0 4th cleavage 



Fig. 8-2. Graphs, modified from Blum and Price (1950), to show the recovery of 

 Arbacia eggs from the effects of ultraviolet irradiation. Eggs were irradiated at 

 various times and the time in minutes between a given pair of cleavages was plotted 

 against the time from irradiation to the cleavage beginning the interval in question. 

 The open and solid symbols represent different experiments in which radiation was 

 given at different times. The points are approximately the center of distribution 

 of a whole series of points given by Blum and Price (1950). (a) Irradiation after the 

 first cleavage. (6) Irradiation h^efore the first cleavage. 



eggs were irradiated after fertilization, often after the first cleavage. 

 Eggs irradiated early in a cleavage interval showed a maximum effect on 

 the duration of that interval, while those irradiated late in an interval 

 showed no effect until the succeeding intervals. By plotting the length 

 of the interval against time from irradiation to the cleavage beginning the 

 interval, a smooth curve showing recovery from the effect was obtained 

 (see Fig. 8-2). The smooth form of this curve and its extension over more 

 than one division interval suggests that the recovery process was inde- 

 pendent of the occurrence of cleavage. Recovery was also demonstrated 

 to occur in eggs irradiated before cleavage. Blum . . . Loos (1949) 

 state in an abstract that X-irradiated eggs behave in the same way as 

 those exposed to ultraviolet, but they give no details. 



The results of Blum and Price (1950) are in agreement with those of 



