DEGENERATE (APYRENE) SPERM-FORMATION OF MOTHS. 477 
which the fusion of acrosome and nucleus is brought about 
is difficult to understand. Whether it is caused by some 
intermediate body, or by mechanical means can only be 
ascertained with a very small degree of probability, but my 
work on the snail and other forms leads me to believe that 
even if adherence is brought about by some intermediate 
substance, the efficiency of this latter substance is improved 
by either the fixation of the acrosome upon the nucleus, 
like the ferrule of a walking-stick, or by the wedge-like 
embedding of the acrosome into a cavity in front of the 
nucleus (Helix). One is led to conclude that in the moth 
it is only after or when the nucleus of the sperm has become 
elongated that complete fusion with the acrosome becomes 
established. PI. 26, fig. 9 seems to show that this fusion 
depends on the nucleus and not on the acrosome. 
The Centrosome. 
In the normal stages of spermatogenesis, the centrosome 
from which the axial filament grows, becomes applied to 
one side of the nucleus and in most forms becomes modified 
in some special manner. It may become flattened upon the 
nucleus, or squared off as in some mammals. In some cases 
it may not appear to have actual physical continuity with 
the nucleus. In Lepidoptera the centrosome becomes 
cushion-shaped upon the nucleus and as the latter elongates, 
the central corpuscle also becomes drawn out slightly. In 
those cases where the nucleus fails to become fixed upon 
the centrosome, the latter eventually forms the head of the 
sperm (PI. 26, figs. 5 and 12.) As far as I can ascertain from 
my sections the centrosome loses its spherical shape (see PI. 26, 
fig. 2) and becomes elongate as in PI. 26, figs. 7 and 8. Meves > 
figures of abnormal stages support this view. One concludes 
from this that the centrosome per se, goes on with its 
slight changes even though the nucleus has drifted aside. 
This is in accordance with what happens in other cell 
elements, which appear to go on developing with at least 
partial independence. It is well to notice that after the 
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