Hazen: Lire HISTORY OF SPHAERELLA LACUSTRIS 219 
I have been unable to find a record of the production of more 
than eight megazooids in one cell and it has even been stated in 
some of the text-books that when more than four daughter-cells 
are produced they are to be regarded as microzooids. Neverthe- 
less I have frequently found in one cell-wall sixteen typical mega- 
zooids, each possessing a distinct cell-wall and in point of size 
equaling and sometimes surpassing the individuals produced in 
groups of four and eight (Fig. 23). Division often begins before 
there is any appreciable increase in the size of the cell-mass (Fig. 
2), but very soon so much fluid is taken in by endosmosis that 
the cell-wall is distended until its outer layer is ruptured or soft- 
ened and an inner layer is pushed out, doubling the original space 
(Fig. 46). That the amount of distention is not dependent on the 
amount of increase in the size of the daughter-cells is indicated by 
the fact that often much more space is formed than they can fill 
(Fig. 5). Probably this distention is of service also in rendering 
the membrane thin enough so that it can be ruptured easily when 
the zooids escape. Generally, however, this part of the cell-wall 
remains considerably rigid, for when, as sometimes happens, only 
a small slit is made for the escape of the zooids they are unable to 
stretch it, but are themselves compressed into a dumb-bell shape 
in squeezing out (Fig. 34). 
It is said by both Cohn and Braun that the daughter-cells 
possess no cell-wall at the time of escape from the mother mem- 
brane. Parker ('93) states that the cell-walls and cilia of mega- 
zooids are formed sometimes before, sometimes after they leave 
the mother-cell-wall In a great number of cases of division into 
four, eight and sixteen daughter-cells, the cell-walls have been dis- 
tinguishable at the moment of escape, if not some time before ; in 
other cases only the deceptive line of color refraction can be dis- 
tinguished outside the boundary of the protoplasmic mass, but so 
delicate a structure might easily escape observation under ordi- 
nary objectives. As for the cilia it is difficult to imagine how 
the zooids could swim away from. the mother-cell-wall if they 
were not formed before the escape. 
