The Coefficient of the Dredge. 
281 
Table I .—Results of determination of coefficient of net. 
Date. 
Pairs 
of 
catches. 
No. of 
resulting 
ratios. 
Counted 
fraction 
of catch. 
Catch op Tube. 
Catch op Net. 
Max. 
Min. 
Max. 
Min. 
1895, May 14....... 
4 
16 
1-10 
2,910 
2,400 
4,760 
2,920 
Oct. 12....... 
4 
16 
1-5 
1,482 
1,170 
2,292 
1,770 
Oct. 25....... 
6 
36 
1-10 
8,490 
4,290 
14,520 
10,560 
1896, Feb.25....... 
5 
25 
1-4 
1,420 
760 
3,500 
1,750 
May 18....... 
5 
25 
1-10 
5,940 
4,310 
12,100 
10,480 
July. 11...... 
5 
25 
1-15 
4,215 
2,430 
8,370 
5,680 
Total........ 
29 
143 
Minimum Ratio; Tube : net : : 21 : 100. 
Maximum Ratio; Tube : net : : 100 : 100. 
Average Ratio; Tube : net : : 49.85 ± 1 : 100. 
Area of opening of tube : area of mouth of net : : 1 : 4. 
Hence coefficient of net = 2, approximately. 
Area of opening of net == 314.1 sq. cm. 
Hence to state catch of net in terms of sq. meter of surface, multiply catch by 
10 000 
X 2 = catch X 63.6, which factor was used. 
«£L4.1 
In determining the number of Crustacea caught by tube or 
net, each species was counted separately. The individual species 
show just about the same amount of variation as does the total 
catch; although in the case of less abundant species the maxi¬ 
mum number caught was not infrequently three times the mini¬ 
mum. In the case of the tube no difference could be detected 
in the range of variation of the numbers of species which are 
active, like Diaptomus, and those which, like Chydomes, or Cy¬ 
clops, are relatively slow in their movements. During the sum¬ 
mer of 1896 an attempt was made to determine the coefficient 
of the dredge from the number of spherules of Gloiotrichia, but 
as this plant is found mainly in the uppermost strata of the 
water on calm days, it proved an unsuitable object, and its 
variations in number in successive catches wore greater than 
those of the Crustacea. 
It may be added that there was no constant position of maxi¬ 
mum or minimum catch in any series which was made, but the 
numbers varied in a wholly irregular fashion. 
