554 



filter-paper catches, Illinois river— Continued. 



O Of 



tn c 



" 2 



Q 





o 

 H 



H 





W a 





5.S 



& <u 



o o 







1 



899 

















22,821 d 



1. 



I 



1000 



04 



40 



82.00 



32.80 



7.20 



0.22 



22,826 d 



IO, 



1 



1000 



025 



25 



86.00 



21.40 



3.60 



0.15 



22,828 d 



17, 



1 



1000 



05 



50 



95-50 



47-75 



2.25 



0.50 



22,831 d 



24, 



1 



1000 



045 



45 



99.00 



44-55 



•45 



0.03 



22.833 d 



3i. 



1 



1000 



04 



4o 



99.00 



39- 60 



.40 



0.01 



22,838 d 



7. 



11 



1000 



05 



5o 



98.00 



49.00 



1. 00 



O.II 



22,841 d 



14, 



11 



1000 



05 



5o 



90.00 



45.00 



5.00 



1. 15 



22,845 d 



2| . 



11 



1 000 



05 



5o 



60.00 



30.00 



20.00 



1.92 



22,847 d 



28, 



11 



500 



4i 



820 



99.99 



819.92 



.08 



0.07 



22,850 d . 



7, 



111 



500 



20 



400 



99.90 



399.60 



.40 



0.54 



22,853 d 



14, 



111 



1000 



16 



160 



99.90 



159.84 



.16 



0.35 



22,856 d 



21, 



111 



1000 



23 



230 



99.80 



229.58 



.42 



0.21 



22,858 d 



28, 



111 



1 000 



04 



40 



99.80 



39-92 



.08 



O.OI 









Average . . 





3.16 



0.41 















undetermined extent invalidated by the errors above noted, I 

 wish to call attention to the fact that they may still serve to 

 indicate in some degree the extent of the leakage and its sea- 

 sonal distribution — conclusions which are in some measure 

 corroborated by the results of enumeration. The ratios of the 

 volumetric determinations of the plankton by the silk and fil- 

 ter-paper methods in August December, 1896, in 1897, in 1898, 

 and in January-March, 1899, as shown by the averages, are 

 respectively 1 to 4.1, 1 to 3.6, 1 to 2.6, and 1 to 7.7, or, averaging 

 all collections, 1 to 3.3. If these figures approach the actual loss 

 by leakage it becomes a matter of some volumetric importance. 



An examination of the table reveals the fact that in a third 

 of the cases the estimated plankton in the filter catch is exceed- 

 ed by that of the silk net. It will be seen that most of these 

 cases occur in instances of small plankton, where the tendency, 

 above noted, to overestimate the silt is most effective in caus- 

 ing this apparent deficiency. In all cases the total filter catch 

 greatly exceeds the total silk catch per m. 3 (cf. Table III. and 

 the one under discussion). 



In general the preponderance of the filter catches is greatest 

 in the warm season of May-September, the growing period of 



