214 Hazen: Lire HISTORY oF SPHAERELLA LACUSTRIS 
while the distended cell-wall of the zooid gradually softens and de- 
composes. At the end of a long cycle of generations the cells 
have only a small central globule of haematochrom, but as the 
permanent resting stage advances the haematochrom increases 
from the center toward the periphery, the color passing through 
shades of golden green and brown (Fig. 18), until the whole cell 
is of the blood-red color of the original individual (Fig. 19). 
Such resting-cells do not develop further—except to increase in 
size—unless desiccation or freezing takes place. 
If these cells are dried or subjected to a low temperature, even 
for a short time, and then again supplied with water, a new cycle 
of development begins. This may proceed in just the same way 
as the former cycle; under certain conditions, however, which 
have not been fully determined, the red resting-cell may divide 
into a number (4, 8, 16, 32) of microzooids which, unlike the 
megazooids, swarm actively within the mother-cell-wall for some 
time before coming out (Fig. 20). These microzooids shoot 
through the water in a very erratic manner; their shape is nar- 
rowly cylindrical or fusiform (Fig. 21), or somewhat ovoid in case 
their movement is less rapid; they have no visible cell-wall and 
their period of motility is much shorter than that of the mega- 
zooids. Many microzooids soon die, others come ‘to rest, secrete 
a cellulose investment and probably grow into normal resting cells 
(Fig. 22). 
HABITAT AND DISTRIBUTION 
Sphaerella lacustris is reported as very common and widely 
distributed in Europe, where it is found from Scandinavia to 
Venice. It seemed quite probable, therefore, that investigation 
would prove an equally wide distribution in America, even though 
Wolle, in his Fresh Water Algae of the United States, was unable 
to furnish any information as to its occurrence here. 
"Inquiry among leading botanists and zodlogists has shown 
that the alga is distributed from Vermont to Texas and from 
Massachusetts to Nebraska (Professor C. E. Bessey) and probably . 
farther west. All the specimens mentioned below, obtained from 
widely separated stations and from different types of habitat, I have 
kept under observation in cultures until there was not the slightest 
doubt that all were referable to the one species, Sphaerella lacustris. 
