No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 367 
media: immature ova of Sphaerechinus , placed in sea water to 
which 1.5 gr. NaCl had been added, show artefacts in the 
nucleolus: “ Each [body] consists of an outer darker shell, 
which is filled with a clear fluid, and the center of each sphere 
is occupied by a small black granule”; several of these struc¬ 
tures are usually found on each section through the nucleolus. 
(For previous descriptions of somewhat similar productions, cf. 
Ransom (’ 67 ), Leydig (’88), and O. Schultze (’ 87 ). The upper 
of the two figures numbered “24” in Morgan’s plate should 
be “23,” since it refers to the nucleolus.) 
Rohde (’ 96 ), ganglion cells of Doris and Pleurobranchus : the 
nucleoli wander out of the nucleus and finally into the neuroglia, 
and there acquiring an envelope (derived from the neuroglia) 
form new cells. [Judging from his figures, however, these 
supposed nucleoli would seem to be myelin drops.] 
Wagner (’ 96 a), spermatogenesis of Arachnids: “ Bei der 
ersten Spermatocytentheilung theilt sich der Nucleolus ent- 
weder in der Ebene der Aequatorialplatte mit den Chromo- 
somen zusammen, oder ausserhalb derselben neben einem der 
Spindelpole. Im letzteren Falle tritt er nach dem Ver- 
schwinden der Kernhiille . . . aus dem Kerne heraus.” 
Wheeler (’ 96 ) gives no description of the nucleoli in the text, 
but he figures several stages of the development in eggs of 
Myzostoma (Figs. 9, 10-1$, M. cirriferum ; Figs. 23, 52-54, 56, 
M. glabruni). In M. cirriferum (Figs. 12-15) * s figured, in 
addition to the single large nucleolus, also one smaller nucleolus. 
E. B. Wilson (’ 96 ) states of the true nucleoli or plasmo- 
somes : “ There is strong evidence that the true nucleoli are 
relatively passive bodies that represent accumulations of reserve- 
substance or by-products, and play no direct part in the nuclear 
activity.” In germinal vesicles he assumes that the “ principal 
nucleolus ” is chemically different from the nucleoli of somatic 
cells ; but that the “ accessory nucleoli ” of the former corre¬ 
spond to the nucleoli of the latter. He concludes that “ we can 
hardly doubt the conclusion of Hacker, that the nucleoli of the 
germ-cells are accumulations of by-products of the nuclear action, 
derived from the chromatin either by direct transformation of 
its substance, or as chemical cleavage-products or secretions.” 
