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THE AMERICAN NATURALIST [Vol. XLVI 



of Lincoln, Nebraska. This portion of the flat has for 

 years been used as a dump, having been filled in several 

 feet in depth mainly with compost. Two years previ 

 ously a heavy summer flood had excavated a cavity, the 

 size of a village lot, to the original alkali bottom, and in 

 this cavity the pool remnant, to the depth of about one 

 foot, remained. The water was dark brown with alkali 

 and the essence of compost, but it suited Asplanchna 

 exactly, for while almost no other plankton was present 

 the Asplanchnas were so abundant as to almost touch one 

 another; the sweep of a yard with a 20-inch dip-net 

 brought up a double handful of the strained animals. 



My original study was confined to material from this 

 single collection because, a day or two later, a heavy rain 

 flooded the pool, killing the Asplanchna to the last 

 individual. 



The collection in question contained two distinct types 

 of Asplanchna. The dominant form, outnumbering the 

 other several hundred to one, was of a large humped 

 type, closely akin to Asplanchna amphora. I shall, how- 

 ever, postpone a detailed discussion of the species, as it 

 is intricate, and unfortunately involves some controversy, 

 while the interest in the phenomena which I wish to 

 describe is not specially dependent upon it. Eeference 

 to Fig. 1 will show fairly well its general appearance, and 

 I need but add at present that it was of very large size, 

 frequently measuring 1,500 p in length. 



Sparsely distributed among the mass of these animals 

 was a mammoth rotifer of related yet very different type. 

 It was saccate, or, more truly, campanulate, in form. Its 

 robust body, without humps, somewhat exceeded in length 

 that of its more slender companion, while its enormous 

 ciliated wreath or corona was extended beyond all limits 

 that the writer ever expected to see in a rotifer. Its 

 transverse diameter frequently equaled the entire length 

 of the animal. This massive giant swam about with a 

 typical though rather slow Asplanchna movement, vibrat- 

 ing or flapping first one portion and then another of the 



