No. 2.] PLASTOGAMY OF ACTINOSPHARIUM. 272 
is a rare event. Among the many specimens that I have 
examined I have not found a single instance of it. 
Instances of apparent karyogamy are numerous. One fre- 
quently finds nuclei in contact, and often the contact is so inti- 
mate as to be suggestive of incipient fusion. But the use of a 
good oil-immersion lens (Zeiss’s 3mm. apochromatic) has never 
failed to reveal a nuclear wall between the two. The nuclei thus 
seen in contact are by no means always two in number; some- 
times four or more are bunched together. But one never finds 
a giant nucleus, as would of course be the case if complete 
coalescence of several occurred. Furthermore, nuclei are 
found in contact, not only at time of plastogamy, but also at 
time of division, and in the ordinary resting state of the animal. 
There are, therefore, strong reasons for believing that fusion 
of nuclei does not take place ; at any rate it can have no signifi- 
cance with reference to the plastogamy. 
I have stated that coalescence is often followed promptly by 
division, and the same observation has been made by others 
(Cohn! Cienkowski,? Brandt?). It has often seemed to me 
that a disturbance amounting to a loss of equilibrium in the 
vital economy of the organism was induced by plastogamy; for 
not only is it often followed quickly by division, but frequently 
by almost amoeboid changes of form. The division in turn 
may be promptly followed by recoalescence. In one instance, 
three individuals were found to be slightly adherent. Three 
and one-half hours later, coalescence was almost complete. 
Two hours and twenty minutes more, and the zygote was far 
advanced in binary division. Complete division, however, was 
not seen. The following morning, sixteen hours later, I found, 
to my astonishment, that complete recoalescence had taken 
place. The composite thus formed persisted for two days, 
once showing a strong tendency to tripartite division, the 
endoplasm being for a short time separated into three masses. 
But the actual division did not take place until three days after- 
ward, and was binary. 
1 Loc. cit., p. 67. 
? Arch. f. mikr. Anat., i, p. 229, 1865. 
3 “Ueber Actinospherium eichhornii,” p. 34, Halle, 1877. 
