SPERMATOGENESIS OF EUSCHISTUS 765 
sunk into the nuclear cavity. Chubb (’06) has criticized my view 
that the ground substance of the plasmosome may be of cyto- 
plasmic origin; but then he was admittedly unable to trace its 
first origin in oocytes of Antedon, and considered it especially 
in later stages when it has a chromatin envelope. 
After the plasmosome has separated from the nuclear membrane 
it becomes for a second time connected with the autosomes, and 
in such a way that the latter radiate towards and end upon its 
surface; in its later history, accordingly, it would seem to stand 
in closer metabolic relation with the chromatin than before. 
Maziarski (’10), in a detailed study of the plasmosomes of gland 
cells, considers them to have the function of elaborating true 
chromatin to take the place of that eliminated into the cytoplasm. 
It may be of service to characterize and define the various kinds 
of nucleolar structures of metazoan cells, for there is still much 
confusion regarding them. As ‘nucleolar structures’ are here 
meant all the larger, generally more or less spherical, inclusions of 
the vegetative nucleus, with the exception of the two following 
that are of strictly chromosomal nature: karyosomes, which are 
thickenings of the nuclear reticulum, and allosomes, or modi- 
fied chromosomes. Leaving out of consideration the karyo- 
somes and allosomes, nucleolar structures may be classified as 
nucleoli and as karyospheres. 
Nucleoli are bodies that do not contain the nuclear reticulum, 
and from which chromosomes do not emerge. They may be 
subdivided into three groups, according to the distinctions made 
by Carnoy in 1884 which the modern researches are tending to 
corroborate. (1) The ‘plasmosomes’ of Ogata, correspondent 
with Carnoy’s ‘nucléoles plasmatiques’ and my true nucleoli; 
these are always acidophilic. (2) ‘Chromatic nucleoli’ or ‘chro- 
matoids,’ correspondent with Carnoy’s ‘nucléoles nucléiniens;’ 
they take chromatin stains, sometimes more intensely than 
the chromatin, but often with a different tone of color. It is 
only by a study of their history and fate that we can distinguish 
between these and karyosomes. Chromatoids are often opposed 
to plasmosomes to compose so-called ‘double nucleoli,’ as in 
germinal vesicles of certain annelids, molluscs and arthropods. 
JOURNAL OF MORPHOLOGY, VOL. 22, No. 3 
