NiGir2.5] CENTROSOMES IN THE ANNELID EGG. 187 
of the secondary and these in turn arise in a similar manner 
from the tertiary centres. Watasé has seen in the egg of 
Macrobdella “a series of thirteen asters, ranging from a minia- 
ture aster, with a microsome for its centre, to the normal aster, 
with a veritable centrosome.” 
Morgan ('96) found numerous “artificial astrospheres’”’ in 
sea-urchin eggs kept in sea-water to which 1% % salt had been 
added. The salt, he believes, stimulates the living eggs to pro- 
duce these structures. It is interesting that the multiple asters 
appear in the eggs of Chaetopterus immediately after they have 
been deposited in sea-water. The latter probably contains more 
salt than the fluids of the body-cavity of the worm. 
R. Hertwig (95) has shown that minute quantities of strich- 
nine stimulate the production of asters (even amphiasters) in 
the maturated unfertilized egg of the sea‘urchin. No centro- 
somes, however, were found. 
Osterhout (97) has recently described in Equisetum the 
origin of the amphiaster from multiple asters, though no cen- 
trosomes were demonstrable. In the egg of Unio, during the 
metaphase of the second maturation-spindle, a supernumerary 
aster appears, remains for a short period, and then vanishes. 
The interesting question presents itself, — If this supernumerary 
aster contains a centrosome, from what preceding centrosome 
does it arise? If it does not contain a centrosome, the latter is 
not a necessary feature, much less the originator, of the aster. 
Referring to the observations of Reinke, Watasé, Morgan, 
and Hertwig, Wilson says: ‘ All these observations are of high 
interest in their bearing on the historical origin of the centro- 
some; but they do not prove that the centrosome of the normal 
aster ever arises by free formation. On the whole, the evidence 
has steadily increased that the centrosome is to be classed 
among the permanent cell-organs; but whether it ranks with 
the nucleus in this regard must be left an open question ”’ 
(oGell7 py 226) 
1 In the appendix to the second edition of this book on the “ Cell,” Wilson is 
inclined to adopt a conclusion nearly related to that which he maintained in an 
earlier paper ('95), by reason of recent observations which “throw grave doubts 
upon the hypothesis of the universal autonomy and genetic continuity of the 
centrosome.” 
