243 



Incipient stages of this variety appeared also at other times. Burck- 

 hardt ('OOa) 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-w r ater 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 Hyalodaphnia 

 (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 w r hich he calls D. galeata 

 with vars. kahlbergiensis and cederstromii, 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) 



