280 



to the abundance of adults. Our collections, extending over longer 

 periods and being at briefer intervals, indicate, however, that this 

 relation does exist. As above stated, the larvae are most abundant 

 at or shortly after the times of greatest abundance of adults that 

 is, the maxima of the recurrent pulses. Apstein also states that 

 reproduction is periodic and development rapid. Maximum 

 numbers are reported by him in May and September. 



Cohn ( '03), on the other hand, maintains that the " innere Logik" 

 and his data show him that the nauplii reach their greatest numbers 

 just prior to the appearance of largest numbers of young and adult 

 Copepoda. His data are from 12 collections between May 1 and 

 October 1 , and favor his contention in 2 out of 3 cases (of maxima) , 

 and both of these lie in collections at intervals of 15 to 16 days. In 

 the light of our data obtained at briefer intervals and the conclusions 

 therefrom that the pulses of larvae tend to coincide or follow at a 

 brief interval those of the adults, it becomes questionable whether 

 his data are sufficient for his conclusion. His logic also overlooks 

 the fact, apparently, that smaller numbers of larvce might lead to 

 coincident maxima of grown forms during a period of abundant 

 food, on which all pulses must be based, since the larval stage may 

 be at such times a brief one and the adult a relatively longer one, and 

 the cumulative effect of this relationship would make the conditions 

 shown in our data logically possible. Furthermore, Cohn used a 

 No. 12 silk in his plankton net, and this allows many nauplii to 

 escape, and probably accounts for the fact that the ratio of larvas 

 to grown forms in his figures is only 1.3 to 1, while in our records it 

 is 3.5 to 1. The discrepancy arising from this leakage may further 

 tend to weaken his data for his conclusions concerning the relations 

 of larvas and adults. 



Steuer ('01) finds that the nauplii in the Danube at Vienna 

 reach maxima in June and in August, but his data are too scattered 

 to fully delineate their fluctuations. Two out of three of his max- 

 ima coincide with those of all Cyclops, and the third antedates it 

 (monthly intervals of collection), as in Cohn's data. 



Diaptomus pallidus Herrick. Average number per m. 3 , 11; in 

 1897, 367; in 1896, 87; in 1895, 152; and in 1894, 146. 



This species was recorded in all months of the year but February, 

 though in a larger percentage of the collections and in larger numbers 

 in July-December. Prior to this season the percentage does not 



