192 



Marsh — Limnetic Crustacea of Green Lake. 



diaptomus — continued. 



No. 

 of Coll. 



9.96. 

 10.96. 

 11.96. 

 12.96. 

 13.96. 

 14.96. 

 15.96. 

 16.96. 

 17.96. 

 18.96. 

 19.96. 

 20.96. 

 21.96. 

 22.96. 

 23.96. 

 24.96. 

 25.96. 

 26.96. 

 27.96. 



Total 

 No. 



2,392 

 2,354 

 2,793 

 3,612 

 2,508 

 3,803 

 1,563 

 4,785 

 4,933 

 5,646 

 4,766 

 5,248 

 3,772 

 4,229 

 4,736 

 1,527 

 746 

 490 

 762 



Per cent. 



0-5 



56.52 

 39.50 

 36.17 

 47.84 

 30.30 

 64.16 

 98.91 

 62.90 

 41.60 

 70.86 

 46.37 

 59.18 

 54.72 

 45.40 

 78.21 

 54.49 

 18.23 

 in 0-20 

 42. 



5-10 



25.09 

 33.30 

 24.63 

 37.65 

 47.53 

 19.99 



.13 



9.01 



28.81 



.42 



as. 02 



21.80 

 26.73 

 19.11 



7.43 

 16.76 



7.51 

 meter 



7.35 



10-15 



15-20 



20-25 



25-30 



30-35 



35-40 



10.70 



5.02 



.75 



.50 



.25 



.12 



8.84 



6.12 



.25 



.69 



1.44 



4.76 



28.07 



2.72 



.46 



1.25 



.68 



4.80 



9.74 



2.99 



.30 



.17 



.75 



.17 



10.84 



1.60 



5.58 



.56 



.44 



2.99 



6.42 



3.10 





2.84 



2.52 



.26 







.06 

 2.01 



.19 



2.67 



.13 

 1.33 



.19 

 2.17 



18.06 



i.25 



19.62 



1.87 



2.59 



.57 



.89 



2.27 



15.02 



4.85 



.49 



.98 



4.83 



.78 



6.73 



3.35 



2.35 



3.02 



3.86 



1.09 



6.25 



1.22 



2.04 



3.43 



4.08 



.69 



14.21 



1.06 



.95 



1.01 



.64 



.13 



23.22 



9.27 



2.46 



.11 



.31 



.07 



8.96 



4.39 



.46 



.25 



.13 



.13 



23.58 



4.19 



.26 



.20 



.13 



.26 



6.43 



15.55 



16.09 



23.59 



7.50 



3.76 



9.98 



6.30 



4.20 



5.77 



6.29 



15.75 



40- 



1.05 



5.10 



1.22 



.39 



.16 



.71 



.39 



.60 



1.78 



1.77 



.21 



.91 



.50 



.05 



.04 



.13 



1.34 



2.36 



A glance at PI. VII will show that Diaptomus has a strongly- 

 marked minimum of occurrence in December and in January. 

 There is an increase in February and March, but in both 1895 

 and 1896, the number in May was very small. Diaptomus ap- 

 pears to reach its maximum in the latter part of September and 

 October. In the fall months, the collections consist mostly of 

 mature forms. In the winter months most of them are immature. 

 From the latter part of March to the latter part of May, nearly 

 all are mature, and the females egg-bearing. In June there is a 

 great preponderance of larvae. 



Apstein ('96, 179 and following) states that the maximum 

 period of D. graciloides differs in different German lakes. The 

 time of the maximum occurrence of Green Lake Diaptomi as re- 

 corded above, does not agree with any of his observations. 

 Birge (Birge '95 p. 448) states that the maximum time of Diapto- 

 mus in Lake Mendota is in July. Inasmuch as Diaptomus is very 

 little affected by differences of temperature, as will be shown 

 later, I think these differences in maximum periods are prob- 



