243 
Incipient stages of this variety appeared also at other times. Burck- 
hardt (’00a) does’ not even concede varietal standing to apicata, 
regarding it merely as a form of seasonal or local value. Its occur- 
rence in our plankton when reproduction and growth are most 
active suggests that it may have a growth value, and be in some 
way correlated with the factors involved in its cyclic production. 
Daphnia cucullata var. kahlbergiensis Schoed. appears but once 
in our records—in the plankton of June 11, 1896. 
The D. cucullata group is a cosmopolitan constituent of the 
fresh-water plankton, appearing frequently in the records of Euro- 
pean plankton. Apstein (’96) finds it in lakes in northern Germany 
in April—-October with maximum numbers in July. The seasonal 
limits thus resemble those in the Illinois, but the maximum falls 
at the time of our midsummer decline. Temperatures in these 
German lakes (16.3° C.) do not, however, reach the high levels 
attained in our waters in midsummer. Stenroos (’98) records it in 
several varieties in the plankton of Nurmijarvi See, the helmeted 
varieties being found in midsummer. Zacharias records it from 
the plankton of German ponds. Scourfield (’98) finds it in small 
numbers in Epping Forest interruptedly in April-November, a 
season coinciding with that in the Illinois. Burckhardt (’00) finds 
it represented by five different “forms’’ in Mauensee in the June 
plankton. Marsson (’00) finds representatives of Hvalodaphmia 
(species not given) in the April-June plankton near Berlin. Am- 
berg (’00) states that this species appears in April, increasing to a 
maximum in July-August, and disappears again at the end of 
November, a seasonal course similar in limits but not in maximum 
to that in the Illinois. His data are too scattered to trace the course 
of production with completeness. Seligo (’00), in waters near 
Danzig, finds the species present in June—January, with maxima 
in June-July and October. In the period of maximum summer 
temperatures (16°-21° C.) the numbers decline as in this period in 
the Illinois. In Seligo’s infrequent (two to three weeks’ interval) 
data there are suggestions of minor recurrent pulses in other months. 
Cohn (’03) finds in Lowentin a Daphnia which he calls D. galeata 
with vars. kahlbergiensis and cederstrémi1, and includes all three in 
his enumeration. His investigation covers the months of May— 
September, throughout which these forms appear, rising in a series 
of recurrent maxima on June 26, August 4,and September 2 and 29. 
(17) 
