272 



The surprising fact derived from the examination of our records 

 of this variety of C. viridis, is that the individuals referred to it are 

 predominantly of the male sex. Out of a total of 74,308, 64,883, or 

 88 per cent., are males, 8,542, or 11 per cent., females without eggs, 

 and only 883, or one per cent., egg-bearing females. In so far as 

 these data go, they indicate that this so-called species, or even 

 variety, of C. viridis, in so far as it is based on the lance-like spine 

 of the stylet, is not well founded. This is, it seems, predominantly 

 a male character, though not exclusively so, since females, and even 

 egg-bearing females, are found which exhibit this structure. 



C. viridis var. brevispinosus appears to be confined to American 

 waters. Marsh ('93 and '95) reports it from the larger lakes of 

 Wisconsin and Michigan, and from the Great Lakes, except Lake 

 Michigan. Birge ('95 and '97) finds that it is the most abundant 

 species of Cyclops (except in summer, when C. leuckarti abounds) 

 in Lake Mendota, and the only one reproducing under the ice. His 

 data exhibit a major pulse in May, and a second one, of less ampli- 

 tude, in October, with slight indications of recurrent minor pulses 

 in midsummer, obscured possibly by the massing of his data in 

 fortnightly averages. The seasonal distribution in Lake Mendota 

 is thus much like that in the Illinois River. Marsh ('97) finds the 

 maximum in Green Lake in June at 68-69, and only scattering 

 occurrences at other seasons. E. B. Forbes finds this variety 

 widely distributed in American waters, but never especially abun- 

 dant. 



Cyclops viridis var. insectus Forbes. Average number, 539; in 

 1897, 2,115; in 1896, 949; in 1895, 2,966; and in 1894, 905. It is 

 thus more abundant by two- to threefold in the stable years of 1895 

 and 1897 than in the flood-swept years of 1896 and 1898. 



This variety was found in every month of the year, though 

 predominantly in April-October, when the percentages of the 

 collections containing it were respectively 64, 100, 85, 100, 100, 87, 

 and 76 per cent. In November-March the percentages were only 

 44, 6, 17, 7, and 13. The numbers of individuals are very small, 

 however, from October 1 to April 20, excepting in the autumn of 

 1897, when, with the delayed high temperatures and the great 

 impetus given to plankton development in the stable conditions of 

 low water, the maximum pulse of all our records, 30,800 per m. 3 , was 

 reached on October 5, a pulse of 1,200 following in November. With 



