260 
as clearly as the nauplii and immature forms. In 1898 the adults 
form only 10 per cent. of the total. 
The relation which hydrographic conditions bear to the 
copepodan population may be inferred in part from the comparison 
of years given above, and from the following table, in which are 
given the average number of Copepoda per m.* and the total monthly 
movement in river levels in July-December, 1897 and 1898. 
July August September 
1897 1898 1897 13898" \|-2 W897 9 eeakSee 
Average Copepoda 
[OSI THA. 6 oc 81,543 7,720 | 121 070) | 115080 |) 2615387 \sson920 
Total movement in 
le viel Seeimiet iene 52 7 a 26 sd 0.6 (fig 2 
October - November December 
1897 1898 1897 1898 1897 | 1898 
Average Copepoda | | 
(OVE THN oho nie 128,093) | 28-7285 49,240 | 10,692 15,740 | 7,908 
Total movement in | | 
levels, in ft.... 0.6 3.9 DD D6) On5) | 2.4 
With a total movement of 11.7 ft. in July-December in 1897 and 
nearly three times as much (30 ft.) in 1898, we find copepodan 
population falling off to less than one sixth that of the more stable 
year. : 
Of the total Copepoda in our records for 1894-1899, 78 per cent. 
are nauplu of Cyclops and Diaptomus, 13 per cent. are immature 
Cyclops, and the remaining 9 per cent. are Harpacticide, Diapto- 
mus, and adult Cyclops. Of the twelve forms, Cyclops viridis var. 
imsectus is the most important quantitatively, and includes one 
fourth of the total adult copepodan population, exceeding the 
next in importance, C. viridis var. brevispinosus, by over threefold. 
