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1894, 53,149. On June 19, 1895, the Copepoda attained a vernal 

 maximum of 1,022,476 per m. 3 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. 3 rising above 

 10,000 per m. 3 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 Harpacticida, Cyclops 

 bicuspidatus, C. prasinus, C. serrulatus, and C. modestus appear to 

 be planktonts belonging to the colder part of the year. As a 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 

 denned in stable conditions. Owing to their relatively smaller 

 numbers the adult Copepoda do not show the pulse phenomenon 



( 18) 



