Hazen: Lire History oF SPHAERELLA LACUSTRIS 217 
lulose. (Fig. 1.) By typical resting-cells are meant the entirely 
red cells, in which the vital processes are at a minimum ; for often 
non-motile cells are found, in which considerable chlorophyl and 
pyrenoids and a nuclear area are seen, but these cells represent 
simply a transition between the motile condition and that of com- 
plete rest, or a state of non-motile vegetative propagation. 
The nucleus and pyrenoids are, indeed, present in the typical 
resting-cells, but are hidden by the haematochrom, which, partly 
in solution in oil drops, and partly in micro-crystalline form (Zopf, 
'95), penetrates the whole mass of protoplasm. That some 
chlorophyl also is present, even in the pure red cells, is indicated 
by the researches of Englemann and Zopf.* 
REPRODUCTION 
Reproduction is accomplished in three ways : 
1. By the formation of large motile daughter-cells or mega- 
zooids. | 
2. By the formation of non-motile daughter-cells. 
3. By the formation of smaller motile-cells or microzooids. 
Tur FORMATION OF MEGAZOOIDS: THE FIRST GENERATION 
Alexander Braun(’51) apparently was the first to note that the 
production of zooids under natural conditions occurs early in the 
morning. The time varies with the season of the year. In the 
summer the zooids leave the mother-cell-wall so early that I have 
found it hard to observe the act even by examining the material 
before sunrise. In early spring and in autumn division does not 
often take place in the open air before seven or eight o'clock. 
This variation is undoubtedly to be explained by the difference in 
the time of sunrise ; but that the escape of the megazooids is due 
not to the atttainment of a certain intensity of light, but rather to the 
conditions of temperature is indicated by the fact that megazooids 
may be produced in absolute darkness. When dry material is 
placed in water in the morning and kept dark for a few hours, 
megazooids will be formed in abundance. At a temperature of 
22?—26? C. five or six hours is sufficient time, while at 16?—20? six 
to nine hours may be required. 
* See the section on the coloring matters. 
