MUNSON: SPERMATOGENESIS OF PAPILIO. 
79 
rily imply a new formation of the astral rays. In the immediate neigh¬ 
borhood of the eentrosome the rays are so crowded as to obscure the 
centrosome entirely, and cause a dark cloudy effect which can be seen 
with a magnification too low for the entire aster to be seen. 
The eentrosome .— In specially favorable preparations, the cen¬ 
trosome can be seen with the highest magnifying power as a minute 
dot at the focus of the astral system (pi. 16, fig. 111). It is sur¬ 
rounded by an inner circle of microsomes. At an equal distance out¬ 
side this is a second circle which barely touches the nuclear membrane 
(pi. 15, fig. 75), and outside this a third circle which intersects the 
nucleus (pi. 16, fig. 92). Viewed from the pole the aster appears 
regular and symmetrical, showing the same thickenings of the fibers 
which give the three-ringed appearance (pi. 16, fig. 112). In these 
preparations, which are especially clear, the astral rays seem to proceed 
directly from the centrosome. That being the case, the minuteness of 
the centrosome, i. e., the central granule, is remarkable. If the cen¬ 
trosome were the result of coalescence of many eytomicroSom.es of the 
ordinary kind, it ought to be larger. It scarcely exceeds a single 
mierosome. It is only in the most favorably preserved material, 
consequently, that it with its circle of microsomes can be seen. Fig¬ 
ure 111 and figure 112 (pi. 16) were drawn from material left for fif¬ 
teen minutes in normal salt solution, then transferred to a concen¬ 
trated solution of corrosive sublimate for fifteen minutes more, after 
which a one-percent solution of acetic acid was added and allowed 
to act for ten minutes. Before staining in saffranin, it was left for 
ten minutes in a fifty-percent alcoholic solution of iodine. 
The nucleus .— While the asters have thus been fully developed, 
the nucleus has remained practically unchanged. The distance of 
the centrosome from the nuclear membrane is usually very constant, 
the second ring of microsomes apparently touching the nuclear mem¬ 
brane, which is still as prominent as ever. The nucleus is regularly 
spherical (pi. 15, figs. 78, 86; pi. 16, fig. 92). It is rarely elongated 
in the direction of the centrosonles (pi. 15, fig. 81) ; but on the Other 
hand frequently indented at one pole (pi. 15, figs. 71, 75), or at both 
poles, being compressed laterally (pi. 15, figs. 76, 82). To suppose 
that this indentation is due to a pushing in of the astral rays as they 
shoot out from the centrosome is about as absurd a proposition as 
could well be made — absurd even if no account be taken of the fact 
that such indentation exists often before the rays are developed (pi. 15, 
fig. 84; pi. 16, figs. 90, 91). 
