The Annual Distribution of the Crustacea. 



315 



Table IV.— Continued. 



1896. 



August 1-15 



August 16-31.... 

 September 1-15 . 

 •September 16-30 

 October 1-15 ... 

 October 16-31... 

 November 1-15. . 

 November 16-30. 

 December 1-15. . 

 December 16-31. 



Diap- 

 tomus. 



Cy- 

 clops. 



D. puli- 

 caria. 



D. hya- 

 lina. 



D. 



retro- 

 curva. 



Chy- 

 dorus. 



Diap- 

 bano- 

 soma. 



91.9 



326.8 



3.7 



95.2 



27.6 



406 5 



8.9 



167.0 



209.0 



5.9 



60.9 



57 1 



426.0 



147.4 



125 9 



157.1 



23.5 



120.4 



157.7 



748.6 



108.3 



163.4 



228.6 



3.4 



192 5 



238.6 



263.0 



32.9 



52.8 



364.8 



0.4 



228.0 



199.3 



423.7 



0.4 



48. & 



469.5 



a 



511.5 



92.7 



191.9 



a 



29.8 



267.7 



Scat... 



314.6 



9.9 



62.7 



a 



23.5 



173.9 



Scat... 



266 



a 



69.3 



a 



29.3 



115.5 



Scat. . . 



182.8 



a 



38.2 



a 



24.7 



93.1 



Scat... 



138.9 



a 



281 



a 



Total. 



960.4 



1073.3 



1440.9 



1113.4 



1368.4 



1314.8 



684.8 



537.7 



365.8 



284.8 



In this table maxima are indicated by bold faced type and 

 minima by italics, a, means absent; scat., scattering individ- 

 uals not enough to count. Parentheses indicate that observa- 

 tions were made on a single date in the two week period ; — , 

 indicates no observations. 



Although the general course of the development of limnetic 

 -Crustacea is so nearly the same in successive years, yet the com- 

 position of the crustacean population may differ very widely. 

 This will readily be seen from the tables, and still more easily 

 by the diagrams which show the numbers of the individual 

 species of Crustacea in the different years. A single illustration 

 is given in Figs. 11, 12, and 13. These diagrams represent 

 the average number of the Crustacea in the latter half of Sep- 

 tember, 1894, 1895, and 1896. The area of the circles is pro- 

 portional to the total number of Crustacea, and the size of the 

 •several sectors is proportional to the number of the individual 

 species. It will be seen that while the total numbers are not 

 very widely different, there is a great divergence between the 

 individual species. Diaptomus y for example, is by far the most 

 numerous in 1895, while in 1894 it is the next to the smallest. 

 In 1894, on the other hand, Chydorus is by far the largest; 

 while in 1895 it is not represented at all. D. retrocurva is one 



