DISTRIBUTION OF FOLLICULINA IN 1914. 379 



almost exterminate them. Yet many remained alive here and 

 there so that when large quantities of the Elodea were put into 

 aquaria many free swimmers escaped. Yet these after forming 

 new tubes on the surface of the water did not remain alive but 

 had all vanished September 5, though in such apparently normal 

 environment others had been kept two weeks in captivity earlier 

 in the season. 



Thus while appearing after the middle of July and being extra- 

 ordinarily abundant in August, the Folliculina were all gone about 

 the end of August and no way was found of keeping them longer. 

 Their period of existence in accessible regions of the river was 

 scarcely six weeks. 



In 1913 they appeared before the end of June and a few lingered 

 on to the first of September in nature and were kept in aquaria 

 in a warm room till the 2/th and a few till November 11. 



In 1912 no live ones were found after September 8. This 

 enormous crowding of the waters with free-swimming Folliculina 

 and dense settlements of the case-making Folliculinas during 

 about a month, the last weeks of July and the first of August, 

 coincides with very high temperatures and abundance of micro- 

 scopic plankton in these waters but it is not at all evident either 

 why the Folliculinas should not come earlier, as they did in 1913, 

 or remain later as they did in 1913 and 1912. 



The great rapidity of their colonization of large areas suggests 

 either very great immigration or else very rapid multiplication, 

 or combination of both. As all material searched in the daytime 

 in 1913 failed to show more than a few cases of multiplication, 

 most all the free-swimming forms being merely the case-making 

 forms again freed, material was collected at all times of the night 

 in 1914, but here again but few cases of division were observed. 



Hence it seems unlikely that fission of a few immigrants actually 

 produced the vast numbers found on the leaves of plants, and it 

 is probable that very large numbers came into the river suddenly 

 from some outside source and these settling down, migrating out 

 again, and in some cases increasing by fission, gave rise to the 

 succession of dwellings covering the leaves for some two months. 



The causes leading to the immigration as well as the causes of 

 rather sudden diminution of numbers and utter disappearance 

 remain entirely unknown. 



