216 AMERICAN MIDLAND NATURALIST. 
aquaria in dense masses leaving little room in a jar, it must 
be remembered that they do so only after they have made their 
environment favorable by counteracting all adverse influences. 
Large quantities of algae can never be kept in the laboratory 
unless they appear of their own accord. Conjugatae are es- 
pecially difficult. Ulothrix is out of the question as are all 
