178 



typical character is corroborative of the view, though not conclusive, 

 that we are dealing with a single species and not with several. 



This species has not been widely reported in the fresh-water 

 plankton. It is evidently a planktont of warmer waters, and for 

 that reason may have escaped notice, since the cooler waters have 

 been the more thoroughly explored. Thus it was not found by 

 Weber ('98) in Swiss waters in his thorough explorations about 

 Geneva, nor by Jennings ('94, '96, '00) in the Great Lakes or inland 

 waters of Michigan. It has, however, been recorded by Skorikow 

 ('97) in the plankton of the Udy River, in Russia, where it was 

 exceeded in number by only two species of its genus, B. pala and 

 B. angularis, ranking tenth in numbers among all the rotifers. His 

 data of frequency from July to October suggest several recurrent 

 pulses. It has likewise been found by Lauterborn ('98) in the 

 plankton of the Rhine, where he classes it with the stenothermal 

 planktonts. Zacharias ('98) finds it in ponds near Leipzig, and it 

 was originally described by v. Daday ('85) from Hungarian waters, 

 and again noted there by Kertesz ('94). Fuller exploration of the 

 summer plankton in warmer regions will doubtless extend the record 

 of its range. 



Brachionus militaris Ehrbg. Average number of females, 147 ; 

 of eggs (carried), 98. In previous years the species was much more 

 abundant, the averages in 1897 being 1,412 females and 523 eggs, and 

 in 1896, 1,288 females and 576 eggs. This greater development in 

 years prior to 1898 is evident in many of the Brachionidcz. 



The following table gives the dates of first and last records in 

 each season, and the location, temperature, and amplitude of the 

 pulses in the several years. 



This is evidently a summer planktont with well-defined limits. 

 These limits appear much less evident in 1898 (Table I.) than in 

 prior years. In 1896 and 1897, for example, the species is almost 

 continuously present in the plankton from the time of its first 

 appearance until the last record for the season. All of the records 

 save two lie above 70, and the average temperatures at which the 

 pulses occur are all at or above 80. Its optimum thus lies near 

 the summer maximum. The lower limits are not definitely 

 established owing to insufficient collections in periods of rise 

 and decline, but they seem to lie near 70, with small numbers 

 lingering to 60. 



