160 
Asplanchna girodi de Guerne 1s reported by Hempel ('99) in the 
backwaters in April. 
Asplanchna herrickt de Guerne.—Average number, 15; in 1897, 
295; in 1896, 317. This species was always rather rare in our waters, 
and is apparently a summer planktont. The earliest record is 
April 29, at 64°, and the latest, November 15, at 48°. There is an 
indication of a vernal pulse in April-May in 1896 and 1897, and the 
recurrence of the species at intervals of a few weeks during the sum- 
mer suggests a polycyclic habit similar to that of other members of 
the genus in our waters, but the data are insufficient to follow the 
cycles if such exist. Ovigerous females were present when numbers 
were greatest, and males and females with winter eggs were found 
at the time of the vernal pulse on May 25 (3,200) in 1897. Hempel’s 
statement (’99) of its rarity in June and July is not borne out by the 
statistical records in these months in 1896, 1897, and 1898. 
This rotifer is abundant in the summer plankton of Lake St. 
Clair, Lake Michigan, and lakes of northern Michigan (Jennings, ’94 
and ’96), and it may be significant that it reaches its greatest devel- 
opment in the Illinois in the spring at 60°-70° and not during the 
period of maximum heat. This is about the summer temperature 
of those northern waters. This species has not to my knowledge 
appeared in the literature of European plankton, though it is found 
in European waters. 
Asplanchna priodonta Gosse.—Average number, 441; winter 
eges, 7. This species is much less abundant in our waters than its 
associate A. brightwellit, being outnumbered by it five to one in 
1898. It is in the Illinois River a summer planktont only, at least 
so far as the records go, though reported elsewhere as perennial. 
The earliest record in any year is April 29, 1896, at 70°, and the latest 
October 5, 1897, at 70°, when an unusual pulse of 22,000 was found. 
The records are too scattered to trace the seasonal history. There 
are only indications of recurrent pulses. In May, 1898 (Table I.), 
the best-defined pulse is recorded. The details, which conform in 
the main to the sequence noted in A. brightwelli of ovigerous females 
with summer eggs during the rise, with males and winter eggs at and 
after the culmination of the pulse, are given in the appended table. 
This is the only cycle found in this year. The presence of 
ovigerous females and winter eggs at other seasons as well, in other 
