229 Hazen: Lire History or SPHAERELLA LACUSTRIS 
THE FORMATION OF  MEGAZOOIDS : THE LATER GENERATIONS 
The second generation is normally produced after the zooid has 
passed through a very short quiescent stage, which is by no means 
equivalent to the regular resting stage since no thick cell-wall is 
formed. 
Most frequently in all generations of megazooids after the first, 
I have found only two daughter-cells produced, but on two occa- 
sions I found that nearly all the megazooids of the second generation 
were produced in fours (Figs. 9, 52). Braun ('51) says this is the 
usual number and that more rarely two or eight are formed. 
It is almost impossible in the later stages unless they are pro- 
duced in drop cultures, to say certainly whether zooids belong to 
the second or a later generation, for the process of formation is 
similar in all cases after the first generation. 
Braun ('51) states that in the later generations division often 
begins before the zooid comes to rest. I once found such a case 
where the mother-cell was swimming rapidly by means of its cilia 
which were still attached to one of the daughter-zooids, although 
each of these was moving independently by means of its own cilia 
(Fig. 38). Perty ('52) says that the cilia of the mother-cell con- 
tinue to move until the protoplasm breaks up into the daughter- 
cells, and Cohn ('50) states that the movement may continue even 
after the cilia are detached from the daughter-cells ; but in cases 
where I have seen these detached cilia remaining they have been 
quite rigid (Fig. 37), and the movement of the cell-wall was caused 
simply by the motion of the daughter-zooids within. 
Perty ('532) has described a figure which he says represents 
division of a motile cell where the anterior part of the cell-wall is 
divided by constriction into two beaks, each of which possesses a 
pair of cilia, while the posterior part is still entire. This, however, 
must be considered a monstrosity, for normally only the proto- 
plasmic part of a zooid is affected by division. 
VEGETATIVE DIVISION 
At the time of his first publication on Protococcus, Cohn (’50) 
undoubtedly thought that the production of non-motile cells from 
resting cells formed a regular part of the cycle of development ; 
he indicates that the contents of the resting-cell divide into two 
