









215 
IMomiGhie yore toe tee A October November Average 
WiGAIr fs ala Peps ase hash jou 1897 | 1898 1897 1898 1897 1898 
Hotalamovement.. 2.2.4) O66 | - 3-9 2D 20 BGP |) sys) 
Average stage......... 2200 | 24286. (2282 TAs | 32 04"|| 35 00 
Average number of C. | 
viridis var. insectus...| 8,625 200 520 68 Be 7098 |) 22 


In 1898, with two and a half times the movement in levels found 
in 1897, the development of tusectus attains less than 6 per cent. of 
the numbers reached in the latter year. 
The occurrences of imsectus in channel plankton exhibit the 
phenomenon of recurrent pulses during the season of its occurrence 
in large numbers whenever collections are sufficiently frequent to 
delimit the pulses. Thus, in 1895 there are such pulses in July, 
August, September, and October; in 1896, in April, June, July, 
August, and September; in 1897, in July, August, September, 
October, and November; and in 1898, in April, May, June, July, 
August, and September, though of slight amplitude in the last three 
months. 
Some of the seeming gaps and irregularities in the series of pulses 
of brevispinosus and insectus will be eliminated if the statistics of 
the two forms are combined in a single series,—a fact which lends 
support to the view that the two forms belong to the same species, 
and are parts of a common group of variable organisms. 
Steuer (’01) concludes from his examination of the plankton 
of the Danube at Vienna, based on 19 (?) collections in 15 months, 
that Cyclops has usually two maxima and two minima in each year, 
and that in the same body of water, owing to various meteorological 
influences, the two maxima do not in any year fall near each other. 
The more extensive data at my command show the limitations of 
such a general conclusion. An examination of the records of ind1- 
vidual species of Cyclops and of the total Cyclopide in our waters, 
make it clear that the major pulses may follow each other at about 
a monthly interval. For example, in 1897, the total Cyclopide 
(19) 
