PROTOZOA AND INVERTEBRATE EGGS 



30: 



RoV)in.son, and Loos (1951 ) do not l)elieve that this applies to Arbacia. 

 Thns there are compelling reasons for thinking that cleavage delay is dne 

 to nuclear damage. The evidence that recovery depends on cytoplasmic 

 events is suggestive but not very strong. 



The situation for the protozoa is not so clear. Hohveck and Lacassagne 

 (1931a, b) found that one of the efTects which occurred in the flagellate 

 Polytoma uvella when it was exposed to a particles was a cessation of divi- 

 sion accompanied by an increase in cell size. The cells failed to recover 

 from this effect and finally died, so it is not clear that the effect should be 

 classified with division delay. Hohveck and Lacassagne do not give 

 detailed data but state that the effect was due to a single-particle event 



100 



80- 



60 



>- 

 o 



40 



20- 



2400 



2600 



2800 

 WAVE LENGTH. A 



3000 



1 



3200 



Fig. 8-3. Action spectra for retardation of cleavage in the sea urchin for irradiated 

 sperm and irradiated eggs, replotted from Giese (1947a). Solid circle = sperm 

 irradiated. Open circle = egg irradiated. 



and that sensitive volume calculations suggested a body the size of the 

 centrosome. Certainly, it would be expected that injury to the centro- 

 some might lead to difficulties with division; but in the absence of 

 detailed data it is hard to judge how compelling is the evidence for this 

 identification. 



Using Amoeba proteus, Mazia and Hirshfield (1951) have found evidence 

 for both nuclear and cytoplasmic effects on division delay by ultraviolet 

 The nucleated halves of bisected amebae are more sensitive to division 



