Hazen: Lire HISTORY OF SPHAERELLA LACUSTRIS 208 
THE Formation oF Microzooips 
Alexander Braun ('51) was apparently the first to distinguish 
accurately the microzooids from megazooids., He found that dur- 
ing the latter stages of the cycle of generations many cells, instead 
of producing only four daughter-cells, continued to divide so as to 
produce a mulberry-like mass which was finally broken up into 
sixteen or thirty-two minute cells. These “ microgonidia" then 
began swarming actively within the mother-cell-wall and finally 
burst out; they were of longer shape than the large swarmers, 
only about 6.6 microns long, of yellowish green color with red- 
dish ciliated points ; they did not increase in size or acquire a 
perceptible membrane but most of them died after coming to rest ; 
others turned into little red globules whose further development 
was uncertain. My own observations as to the character and man- 
ner of formation of the microzooids agree with Braun's account. 
Sometimes a zooid which has recently come to rest appears to be 
forming four megazooids but further watching discloses eight or 
sixteen active microzooids (Figs. 24, 25). I have, however, found 
microzooids developed most abundantly from red resting-cells which 
before being dried had been subject to unfavorable conditions (Fig. 
20) The shape of microzooids varies from fusiform or cylindrical 
when they are most active to ovoid when they are more sluggish. 
Their rate of movement, nearly always more rapid than that of meg- 
azooids, is perhaps to be explained by the fact that their cilia are 
as long as those of megazooids while their bodies are much smaller. 
The color varies with that of the mother-cells from which they are 
produced, but usually when considerable of the yellowish green 
color is present the red pigment does not form a central mass as 
in megazooids but is collected at the anterior end (Fig. 28) or in 
a central girdle (Fig. 26). The movement of one brood of micro- 
zooids appears never to continue longer than through one day, 
though a new brood may be produced from other resting-cells 
in the same vessel on successive days for a week. Generally 
most of the microzooids die but sometimes after coming to rest 
they. acquire a thick cell-wall and gradually increase in size as 
they grow red. I have been unable to develop them further. 
By supplying nutriment to these red globules in Van Tieghem 
cells, Rostafinski (75) succeeded in causing them to increase to 
