265 
Stable hydrographic conditions appear to favor the increase in 
C. bicuspidatus, as is seen in the large pulse of November 15,-1897 
(3,560),and the shght pulse (240) during declining levels in February, 
1899. 
The vernal development of 1898 (Table I.) is distinctly pulse-like, 
and there are traces elsewhere of similar phenomena, but 1n general 
the numbers of C. bicuspidatus are too small to exhibit clearly the 
phenomenon of recurrent pulses. 
Of the totals of all individuals recorded 1n 1894-1899 I find that 
37 per cent. are males, 16 per cent. egg-bearing females, and 47 per 
cent. females without eggs. Immature forms and nauplii were not 
distinguished from those of other species. With the exception of 
a few stragglers, the egg-bearing females were limited principally 
to March-May. In exceptional cases the males greatly outnum- 
bered the females, as on November 15, 1897, when the ratio was 
2,820 to 680. 
Though apparently widely distributed, this species does not 
appear frequently among the planktonts reported from European 
lakes. Scourfield (’98) reports it as a common species in the waters 
of Epping Forest throughout the year with the exception of a period 
of absence or depression in July—August, and Scott (’99) finds it in 
shore collections made in various months of the year in Scottish 
lakes, and more abundantly in the warmer months. It has been 
reported in the potamoplankton in Europe only by Rossinski (’92) 
from the Moskwa, by Zernow (’01) from the Schoschma, and by 
Volk ('03) from but one of seven localities in the Elbe at Ham- 
burg. 
In American waters, on the other hand, C. bicuspidatus is more 
abundant, and in the Great Lakes it forms a very important part 
of the plankton. Forbes (’82) finds it (as C. thomast) to be the 
dominant Cyclops in the summer plankton of Lake Michigan and 
(790) also abundant in that of Lake Superior. Marsh (’93 and ’95) 
finds it in the summer plankton of the Great Lakes, near Charlevoix, 
in Lake St. Clair, the Detroit River, and Lake Erie, but only rarely 
and in small numbers in the smaller bodies of water in Wisconsin 
and Michigan. E. B. Forbes (’97) extends its recorded range to 
Massachusetts and to the lakes and rivers of Wyoming, and states 
that it is widely distributed in America and occurs in large ponds 
and rivers. Brewer (’98) reports it in the vernal plankton of deep 
