PROTOZOA AND INVERTEBRATE EGGS 



3io 



lOOn 



readily activated eggs of the marine worm Urechis caupo with this same 

 radiation. 



Harvey and HoUaender (1938) fractionated the Arbacia egg by ceiitrifu- 

 gation into white (nucleated) and red (nonnucleated) halves and separated 

 the latter into yolk and pigment (luarters. Activation was obtained with 

 some differences in detail when either half or either of the two quarters 

 were exposed to ultraviolet of 2480 A or below. Activation was also 

 obtained for the red half and its two quarters with doses of the band of 

 wave lengths 2650-3000 A, which were ineffective with the whole egg or 

 the white half. It can be concluded 

 that the nucleus does not play an im- 

 portant role in activation by ultraviolet. 

 While there seem to be differences in 

 detail in the activation of different parts 

 of the egg, it is not at all unlikely that 

 changes in the surface of the eggs are 

 involved. This is further indicated by 

 the studies of Reed (1943) and Spikes 

 (1944) which have shown localized effects 

 on membrane formation as the result of 

 unilateral irradiation of sea urchin eggs. 

 Similarly, Tchakotine (1935a, b) has 

 shown localized changes in the surface 

 followed by activation phenomena as a 

 result of localized irradiation of the 

 Pholas egg. 



The investigations of Heilbrunn and 

 Wilbur (1937) and Wilbur (1939) on the 

 effects of calcium and magnesium on 

 ultraviolet activation of the Nereis egg 

 also suggest a surface phenomenon. 

 Heilbrunn and Wilbur (1937) have shown 

 that citrate inhibits the activation ; they 

 suggest that this is due to removal of cal- 

 cium from the cortex, so preventing 

 Heilbrunn's views, is responsible for 



•— 



2200 



2400 

 WAVE LENGTH, A 



2600 



Fig. 8-6. Action spectrum for 

 activation of Arbacia eggs, from 

 HoUaender (1938). 



the calcium release which, on 

 the activation. Alsup (1941) 

 found that photodynamic activation of Nereis eggs by visible light in 

 the presence of eosin or rose bengal was likewise inhibited by 

 citrate. Wilbur (1939) has shown that magnesium inhibits activa- 

 tion by small doses of ultraviolet but the inhibition is overcome by 

 larger doses. Calcium antagonized this action of magnesium. It was 

 suggested that magnesium acts in the same manner as calcium but less 

 efficiently. 



Excystment of Protozoa. The process of excystment in the ciliate pro- 



