80 
somewhat erratic. It has occurred in every month from February 
through October, but in smaller numbers and sporadically in the 
colder months. In 1898 its seasonal curve is of characteristic form. 
It makes its appearance March 15,and 1s continuously present until 
the end of September. There is a vernal maximum April 26 of 
240,000, but no corresponding autumnal one. In 1898 there are 
indications of recurrent pulses at brief intervals which coincide in 
location immediately or approximately with similar ones of Gonium 
and Pandorina. These pulses occur March 15 (3,600), April 5 
(2,800), April 26 (240,000), June 14 (60,000), August 2 (8,000), 
August’ 23 (3,200), and September 20 (2,000). The minima 
between these pulses in all cases but one fall below 1,000. In 
1897 a vernal pulse was not detected, a maximum of 496,000 
occurring August 31, and but three minor pulses appearing. In 
1896 this species appeared in the plankton on February 20,- 
and remained until the end of August with a month’s interrup- 
tion in May-June. There were no marked pulses, exceeding 
15,000, in that year. The absence of the spring feoda Pie 
Pl. X.) and the disturbed hydrograph of the summer may account 
for this suppression of development in Eudorina. The distribu- 
tion in preceding years is also irregular. 
Eudorina begins its seasonal development at temperatures but 
slightly above 32°, but any considerable growth is not attained 
until at least 45° has been reached, and the largest pulses on record 
have been at the close of the period of maximum summer heat at a 
temperature of 80°, and the vernal pulses have been at 60° or above. 
The disappearance of EHudorina from the plankton in the early fall, 
about the time that foliage is killed by autumnal frosts, has been 
constant in the different years. 
Eudorina is not sufficiently abundant to be of any considerable 
importance in determining directly the volume of the plankton. 
It serves as food for many of the rotifers, and is itself frequently 
parasitized by Dangeardia mammullata Schréder, which destroys the 
cells but leaves the matrix intact. There are times when it is 
hardly possible to find perfect colonies,and when it is not unusual 
to see colonies swimming about propelled by one or two surviving 
cells. 
Euglena acus Ehrbg.*—Average number, 214,807. Found from 
the middle of March till the first of November, and most abundantly 
