259 
1894, 53,149. On June 19, 1895, the Copepoda attained a vernal 
maximum of 1,022,476 per m.’—more than twice the maximum 
record for any other year. 
The Copepoda occur in every collection examined, and throughout 
the whole seasonal range in temperatures. As shown in Table I., 
the copepodan population during minimum temperatures in De- 
cember—February is at a minimum, the number per m.? rising above 
10,000 per m.* in but 6 instances in 44 collections in these months, 
and falling below 1,000 in but 5. In March—April, as temperatures 
rise, the numbers increase rapidly, especially after 50° is passed, to 
a vernal maximum in the last days of April or early in May, usually 
at the time of the vernal volumetric maximum or very shortly 
thereafter. In fact, volumetric maxima are generally accompanied 
by copepodan maxima culminating at the same time or a week 
later,—as in May, 1898, when the volumetric is on May 3 and the 
copepodan on May 10. 
Numbers continue to be large during the period of summer 
heat, declining somewhat tardily with the autumnal decline in 
temperatures. In midsummer in 1898 numbers fall below 20,000 
in 9 instances in disturbed hydrographic conditions, but in all 
previous years in April-September there are only 9 such records in 
a total of 63. The decline to the winter minimum is usually com- 
pleted in November, though in 1897, 20,000 is not permanently 
passed until December 21, at 32°. 
The Copepoda are thus perennial in the plankton, and the fact 
that they exhibit a larger winter population than the Cladocera is 
due to the fact that a number of species,—the Harpacticide, Cyclops 
bicuspidatus, C. prasinus, C. serrulatus, and C. modestus appear to 
be planktonts belonging to the colder part of the year. Asa whole, 
however, the Copepoda reach their greatest quantitative develop- 
ment in the warmer part of the year, with a major pulse in April— 
May and an occasional autumnal pulse, as in 1897, of equal or 
greater proportions. 
The whole course of the seasonal occurrence of the Copepoda as 
revealed by collections at frequent intervals, exhibits the phenome- 
non of recurrent pulses at intervals of 3 to 6 weeks, and more clearly 
defined in stable conditions. Owing to their relatively smaller 
numbers the adult Copepoda do not show the pulse phenomenon 
(18) 
