12 THE PROTOZOA 



spores escape and swim freely, multiplying by fis- 

 sion ; later on each becomes attached by the end 

 surrounded by the cilia and develops a disc at the 

 opposite end, loses its original zone of cilia, and 

 grows up into an ordinary VorticeUa. 



This process is not of frequent occurrence. 



D. Action of Beagents. 



1. Kill some VorticellcB with osmic acid (1 per cent, or 



weaker). Stain with magenta or carmine, and 

 mount in glycerine, or balsam. 



The nucleus will be stained, and its shape-and 

 relations can be well studied. 



2. Weak solutions of poisons such as acetic acid, corrosive 



sublimate, etc., cause the animal to retract its disc, 

 and the stalk to gradually coil up into a close spiral, 

 and then break off close to the base of the bell. In 

 the natural condition the cell-body may separate in 

 the same way from the stalk and swim away to a 

 fresh resting-place, when scarcity of food or other 

 adverse circumstance renders it advantageous. 



