272 JOHNSON. [Von.Ix 
aqueous solution of corrosive sublimate heated to about 80° C., 
stained with Weigert’s picro-carmine, and sectioned in paraffine. 
Hot corrosive sublimate proved a much more satisfactory kill- 
ing agent than picro-acetic, as far as the preservation of the 
cytoplasmic reticulum is concerned; but in regard to the nuclei 
I could see no difference between the two, It was perfectly 
feasible to embed the specimens in paraffine, and cut unbroken 
series of sections. In this way it was possible to examine zz 
situ every nucleus in the specimen. 
All specimens examined contained many nuclei— generally 
two or three hundred. The greater proportion of the nuclei 
lie in the cortical portion of the endoplasm as originally de- 
scribed by Max Schultze,! but not a few may be found through- 
out the endoplasm—an observation long ago made also by 
Greeff.2. No nuclei are normally found in the ectoplasm, 
although a few are sometimes pushed out into it in the course 
of plastogamic fusion. As is well known from the studies of 
Gruber? and of Richard Hertwig,* the nuclei are variable as to 
structure in different individuals or even in the same animal. 
They sometimes contain a single large central nucleolus, some- 
times two or three of irregular shape, sometimes many. 
Although scattered nuclei different from the majority may 
often be found in the same animal, the different types of nuclei 
— uni-and multinucleolar — are usually characteristic of distinct 
individuals. The structure of the nuclei has been so fully and 
accurately described by R. Hertwig® that I need not enter 
upon further details here. 
A striking and significant fact in connection with the plasto- 
gamy is the entire absence of mitosis. Mitotic phenomena 
almost invariably — perhaps always— accompany karyogamy, 
and it is the rule for nuclei to fuse in some stage of karyokin- 
esis. The work of Gruber® and of R. Hertwig7 has shown 
that the division of nuclei in Actinosphzrium (which is mitotic) 
1“Das Protoplasma der Rhizopoden und der Pflanzenzellen,” p. 35. Leipzig, 
1863. 
ee f. mikr. Anat., iii, p. 397, 1867. 
3 Z. f. w. Z., XXxvili, p. 374, 1883. 
4 Jen. Zeitschr., xvii, p. 494, 1884. 
5 Loc. cit., p. 494. 6 Loc. Cit. p. 374. 7 Loc: cit., p. 491. 
