420) 
such as Thompson’s and Quiver, this marked degree of resem- 
blance is the more striking. 
A comparison of the course of production in Phelps Lake 
(Pl. XL.) and Thompson’s Lake (Pl. XX XVII.) in 1896 reveals 
14 agreements out of a possible 25, or 56 per cent. Of the 11 
disagreements 3 fallin the period of few collections in the au- 
tumn months, when Phelps Lake was reduced to shallow pools, 
and 4 occur during the vernal pulse of April-May. A compar- 
ison of the planktographs and thermographs of the two lakes 
shows that in Phelps Lake the temperature is from 2° to 8° 
higher than in Thompson’s Lake for a period of six weeks dur- 
ing the rise of the vernal pulse. Hence this culminates earlier 
by a fortnight in the former, and in consequence a dislocation 
of the course of production in the two lakes occurs in this peri- 
od. The two planktographs are, however, strikingly alike in 
the fact that in the interval between March 31 and June 1 
there are three pulses of regularly decreasing amplitude in 
both lakes. The similarity is thus greater than the percentage 
indicates. 
A comparison of the course of production in Phelps and 
Quiver lakes (Pl. XL. and XXVII.) reveals 15 agreements out 
of a possible 28, or 54 per cent.—but little more than chance de- 
mands. In this case the environmental differences are greater, 
the effect of spring water, vegetation, and flood invasion inter- 
fering in Quiver Lake with the course of production. 
A comparison with Dogfish Lake, where the disturbing fac- 
tors of spring water and flood invasion are less immediate in 
their action, reveals a slightly greater degree of similarity—16 
out of 28, or 57 per cent. 
In the case of Flag Lake the agreement is still less, being 
only 11 out of 24, or 46 per cent. Itis a noticeable fact that 
the disagreements are most numerous in Quiver, Dogfish, and 
Flag lakes, all of which are rich in vegetation, and these disa- 
greements occur in greatest proportion during the months of 
May-—August, when with changing river stages the proportional 
occupation of these lakes by vegetation fluctuates greatly— 
