186 MEAD. [Vou. XIV. 
and pass more easily from one phase into another; for example, 
the Zwischenkorper and the contraction-band in muscle-cells. 
But the origin and behavior of the asters and centrosomes 
in the maturation of Cheetopterus directly support the interpre- 
tation that the centrosomes arise de novo out of the cytoplasm 
and are resolved into it, and that they are not, therefore, per- 
manent organs of the cell, like the chromosomes, although some 
of them show a considerable degree of persistence. 
Leading up to the formation of the first maturation-amphi- 
aster, there are formed within the egg a large number of distinct 
asters (seventy-five more or less), two of which — the primary 
—come to lie at the poles of the maturation-spindle.! The 
view held by the majority of recent workers that the aster is 
‘formed under the influence of the centrosome,” or the admis- 
sion that the centrosome is in any way a constant feature or 
necessary adjunct of the aster (and without this hypothesis there 
is no force in the permanent-organ theory) offers a dilemma: 
either (a) this cell (the odcyte of the first order) contains a 
very large number of centrosomes which have arisen by the 
division of a preceding centrosome, or (0) it contains a large 
number of centrosomes which have arisen de nxovo out of the 
cytoplasm. If one accepts the first alternative, he must imagine 
a satisfactory explanation of the origin of the many centrosomes 
from a preceding element of the same kind, and of their distri- 
bution to the various portions of the cytoplasm, and must also 
account for the total disappearance of by far the larger portion 
of them. It is hard to reconcile such wholesale disappearance 
with the notion of the centrosome as a permanent and ultimate 
organ of the cell. 
Multiple asters, similar to those in Chzetopterus, have been 
described by Carnoy in Ascaris during the formation of the 
second polar globule, and by Reinke (94) in the peritoneal 
cells of the larval salamander. Reinke groups the multiple 
asters into three classes,— primary, secondary, and tertiary 
mechanical centres, — according to the degree of their develop- 
ment. The primary mechanical centres, which contain a tru¢ 
centrosome, arise by the coalescence and further development 
1 Possibly several coalesce to form each aster (see p. 195). 
