ON EGGS OF MARINE ANIMALS 65 



sectioned egg. Here I take up the simplest and the most com- 

 monly employed method for these preparations, leaving for later 

 consideration my method for preparing special staining. 



Final stages of dehydration 



The final stages of dehydration are important because it is in 

 the alcoholic solutions above 80 per cent that cells suffer most, 

 especially from shrinkage. The changes to successively stronger 

 solutions should therefore be carried out in the minimum time 

 that insures dehydration. Since the eggs become more brittle 

 the longer they remain in alcohols above 80 per cent, one should 

 not prolong their residence in the highest strengths of alcohol — • 

 90, 95 and 100 per cent. Only at the sea-side do I use absolute 

 alcohol; inland, even before clearing with toluene and xylene, 

 I use only 95 per cent alcohol. 



The 80 per cent alcohol is removed from the eggs and replaced 

 by 90 per cent alcohol for 30 minutes. This is removed and 

 replaced by 90 per cent alcohol, again for 30 minutes. The 

 90 per cent alcohol is removed and replaced by 90 per cent 

 alcohol in the same way, except that the two changes are 15 

 minutes each. The second change of the 95 per cent alcohol is 

 now replaced by two changes of absolute alcohol, each acting 

 15 minutes. The absolute alcohol is removed as thoroughly and 

 as rapidly as possible and replaced by an oil used for clearing, 

 xylene or toluene, for example, two changes, acting 15 minutes 

 each. 



Literature 



Just, E. E. 1930. The amount of osmic acid in fixing solutions 



necessary to blacken fat. Science, Vol. 71. 



1933. A cytological study of effects of ultra-violet light on 



the egg of Nereis limbata. Zeitschr. Zellf. mikr. Anat., Bd. 17. 

 Mathews, A. P. 1901. The changes in structure of the pancreas cell. 



Journ. Morph., 15. suppl. 



