22 
usually high), they decline in amplitude, and in November—Decem- 
ber often fail to appear in the small numbers recorded. In 1894, 
records are too scanty to be of significance. In 1895 there are 
three well-defined pulses, and traces of a fourth in August-Novem- 
ber. In 1896 there are five in May—September. In 1897 there are 
six in July-December, data during the remainder of the year being 
insufficient to define the pulses. In 1898 the vernal pulse in June 
and a feeble one in October are the only ones which appear. The 
pulses of Bosmina are best defined in the stable low water of the 
last six months of 1897. During that period they closely approxi- 
mate in location of maxima and minima the quantitative pulses 
and those of the chlorophyll-bearing organisms and of the rotifers. 
(Compare on this point the plates for 1897 in Part I.—Kofoid, ’03— 
and Pl. III. and IV.). The slopes of the pulses indicate that Bosmina 
is capable of very rapid multiplication; and their coincidence with 
other pulses just noted, taken in conjunction with the fact that 
males and ephippial eggs appear but rarely, suggests that these 
pulses of Bosmina are immediately dependent, in large part, upon 
fluctuations in the food supply for their origin and for the varying 
courses which they run. 
The relations of Bosmina to temperature appear in the facts 
that all pulses exceeding 5,000 per m.* in amplitude occur at tem- 
peratures above 70°, that the vernal rise does not proceed with any 
rapidity until this temperature is attained, and that the depressing 
effect of the autumnal decline below 70° is at once apparent in the 
reduced numbers per m.* No constant relation between the pulses 
of Bosmina and the midsummer heat pulses—such as appears in 
the records of Diaphanosoma—can be traced in the occurrences of 
Bosmina. 
An inspection of the accompanying table, in which the mean 
monthly Bosmina population per m.* of channel water in July—De- 
cember, 1897 and 1898, is given, and also the total + and — move- 
ment in river levels for these months in each year, will suggest an 
intimate connection between stability of hydrographic conditions 
and the increase of Bosmina. In 1897 the total movement for these 
months is from five sevenths to one tenth of that in 1898, and in 
every instance the Bosmina population is also greater by from 7.5 
to nearly 400-fold in 1897, the more stable year. The means of the 
six months are 2.03 ft. and a population of 3,691 in 1897 to 5.3 ft. and 
(16) 
