No. 2.] PLASTOGAMY OF ACTINOSPHARIUM. 271 
individuals of Acténospherium etchhornit. "The specimens were 
found in a gathering from Lake Quinsigamond, Worcester, 
Mass., a gathering which had been made two months earlier, 
and in the meantime had stood undisturbed. Much of the 
vegetable matter which it contained had decomposed, and an 
extensive bacterial growth had developed. Early in January 
Actinosphzerium was found in large numbers and of unusual 
size, many of them exceeding half a millimeter in diameter. 
Instances of the fusion of two or more individuals were very 
numerous, 
My observations upon the cytoplasmic phenomena of the 
process do not differ materially from those of Cohn,! Gruber,? 
Penard? and others upon this form and its near ally, Actznophrys 
sol. Two or more individuals come in contact, and the pseu- 
dopodia flow together, forming a sort of network between the 
gametes, as was described by Cohn# for the present species, 
and recently by Penard® for Actinophrys sol. Then the ecto- 
plasms of the gametes fuse, until at length the endoplasmic 
central masses are in contact (Fig. A). Next, the process 
involves also the endoplasm (Fig. 4), till finally the coalescence 
is indistinguishable from 
” 
becomes complete, and the “zygote 
a normal individual (Fig. C). The fusion may take place 
rather rapidly, as was the case in the series represented in 
Figs. dA—-C (1 hour, 50 minutes), or may require two or three 
days. Very frequently it is soon followed by division (Fig. D). 
The process is not essentially different where more than 
two individuals fuse ; but the greater the number, the more 
irregular the resultant “colony,” and the less perfect the 
fusion. These colonies usually undergo prompt multiple divis- 
ion, but not necessarily into the original number of individu- 
als. It is not uncommon, for instance, to see a zygote of three 
individuals divide by a symmetrical constriction into two. In 
these cases there can be no question of the completeness of 
the plastogamy. 
For study of the nuclei gametes in various stages of coales- 
cence were killed either with picro-acetic mixture or saturated 
’ 
U Zak. Ws Zs, Ul, p. 60, L851 2 Z. f. w. Z., XXXvili, p. 62, 1883. 
8 Arch. de Biologie, ix, p. 159, 1889. 
4 Loc. cit., p. 66. 5 OG.tCit., pe Usa 
