No. 2.] PLASTOGAMY OF ACTINOSPHZRIUM. 275 
} (elongated) ss. «7 Siwy sates) wy.’ O:3574M., Mar. 2 
Ze le 8. le wm, ee we we te Pw OLS O ACME, cE  ~3h 
/ Se ae ne a a ee a ae > ee’, 5) ey a 
2 : oes 9 AM, “& -§ 
One isolated. 
9 AM, “ 7. 
Zee ee ee tw ee oe Oy A, PP Oy 
SRC Cut antia So sect 8.35 AM. “ II. 
One isolated ; no change in number till Mar. 31. 
{ (in division) 2% Sa e 4 oe os AO OS Aus @. So, 
Z (OWE FEMOVER) ss. 4 ie 3s we OSES AsMign “31, 
I 9.30 A.M., Apr. 1. 
No increase in number, and died, Apr. 18. 
It is seen from the record that plastogamy is not followed by 
encystment, or any notable reproductive activity. But each 
instance of fusion (e.g. Jan. 15, 25) is very likely to be followed 
by division and considerable increase in number within a day 
or two. 
It has been pointed out by Brandt! that coalescence in 
Actinosphzrium does not necessarily follow from mere con- 
tact. I have in no instance been able to cause it by bringing 
individuals together. Artificial coalescence was, however, 
accomplished by Cienkowski? by amputating a small portion 
from each individual and bringing the wounded surfaces 
together. In this way he was able to cause the successive 
fusion of five individuals to form a compound zygote. 
Since it is impossible to ascribe fertilization to the plastogamy, 
where shall we look for this all-important function in the life- 
history of Actinosphzrium? In Schneider’s® account of the 
encystment of this species, the statement is made that the 
cyst-spores (“kugeln’’) at first contain several nuclei each, but 
afterwards only one. The presumption is that the nuclei 
coalesce; but if such be the case, division must subsequently 
occur, for at the time of escape from the cyst the young 
Actinospherium has several nuclei. F. E. Schulze,t on the 
contrary, found but oe nucleus in each cyst-spore at all 
times; and the later observations of Brandt® go to confirm 
those of Schulze on this point. Brandt, however, found a 
1 Loc. cit., p. 34. 2 LOG. Cit., ps220. 3 2.4. WLn5 2X1, pa S07. 
4 Arch. f. mikr. Anat., x, p. 345, 1874. & Loc. €it., p30: 
