| aa Vol. in cm.3 Departure from 
| 9 | ona: of catch mean in per cent. 
No. Location Time = |3alon ‘ = 
A ==) es) Erek | To- Total Plank- 
2|n ton Silt | tal catch ton 
1 j1m.above Hardin... 5:45-6:45 p.m. | .10) 72 | 60 , .18 +26 44 — 85 — 75 
2 |Kampsville Dam......... 6:45-7:45p. m. -08 | 71 | 80 | .23 91 | 1.14 — 61 — 68 
3 Jlm. aboveC. A. bridge} 4:30-4:45 a. m. .08 | 69 | 90 | lost 
4 |Florence...... ......... 6:00-7:05 a. m. |) .03 | 68 | 99 | .02 |2.32 | 2.34 —wail — 97 
5 \Mauvaise Terres Crk} 7:10-8:10 a. m 04] 68 | 98 | .05 |2,36 | 2.41 — 18 — 93 
6 |Meredosia ......... ........| 8:10-9:15 a, m 04 | 69 | 95 | 11 |215 | 2.26 = 5%} — 85 
7 |La Grange .... 10:00-11:00 a. m 04 97 | .07 |2.21 | 2.28 — 24 — 90 
8 |Beardstown ...... . }11:00-12:00 a. m 04) 88 | .22 |1.61 | 1.83 = 38 — 69 
9 |Browning. .. .. | 2:45-3:45 p.m 05 95 | 11 |2.15 | 2.26 7 — 85 
10 |Holmes Wanding...... _| 3:45-4:45 p. m 05 10 |1.80 20 | 2.00 59) +153 
11 |Havana........... -.... .....| 6:15-7:30 p. m 05 80 | .53 |2.13 | 2.66 =a) = 
12 |Liverpool. -...... --...... 4:20-5:20 a. m 04 167.5) 50 2.12 | 2.12 | 4.24 + 44 +199 
13 |2 m.above Copperas 
Creek ene 5:25-6:30 a. m 041 68 | g0 !1.32 15.29 | 6.61 +125 + 86 
14 |Mackinaw Creek... 7:10-8:20 a, m 05 { 67 | 70 |1.47 | 3.42 | 4.89 66 +107 
15 |6m.above Pekin........ 8:40-9:45 a. m, 06 | 67 | 90 -95 18.59 | 9.54 +224 + 
16 |7m. above Peoria... tanasabupceael 08 | 67 | 60 |2.19 3.29 |5.48| + 86 +209 
17.‘ |Chillicothe Park.. 2:50-1:50 p. m. | .12} 66 | 15 92 16 | 1.08 — 63 + 30 
18 |1m. below Lac 7:30-3:40 p. m. 15} 66 | 20 88 +22 =| 1.10 — 62 + 27 
19 |Henry ....... :00-4:55 p. m. 20] 66 | 88 12 -90 | 1.02 — 61 — 
20 |Hennepin .. :20-6:30 p. m. 20} 66 | 95 | .12 |2.20 12.32 — 21 — 8 
Average | -T1 | 2.23 | 2.94] +57 | +89 
An inspection of the data of this table at first gives little 
comfort to one desiring to establish even an approximate uni- 
formity in the distribution of the plankton along the length of 
the stream. The average departure from the mean is +57 per 
cent. in the case of the total catch and +89 per cent. in the esti- 
mated plankton, with ranges respectively from --85 to + 224, 
a total of 809 per cent.,and from --97 to +209, a total of 306 per 
cent. This is greatly in excess of the figures above given from 
the work of Reighard and of Apstein, and as a whole the data 
are so aberrant as apparently to disqualify them for scientific use. 
If, however, we take into consideration the conditions un- 
der which the collections were made, the aberrancy of this se- 
ries loses its force. In addition to the errors introduced by the 
slight clogging of the net and the uncertainty as to the precise 
distance, there is an error of undetermined proportions caused 
by the vertical movement of the planktonts and consequent 
possibility of uneven distribution at the 18-in. level between 
4:30 a. m. and 7:45 p. m.—the extremes of our time of collection. 
Furthermore, an examination of the planktographs in the 
river and its backwaters for 1896 and 1898 (Pl. X., XIL, 
XXVII., XXIX.,XXXI., XXXII.) —in which years the collec- 
