746 THOS. H. MONTGOMERY, JR. 
118 the autosomes have become so spread out that they compose 
a thin layer of chromatin covering the whole inner surface of the 
nuclear membrane except at the pole nearest the centriole (c). 
From now on boundaries of the autosomes can no longer be dis- 
tinguished. This peripheral mantle of chromatin appears deeply 
stained when viewed in section, but pale in surface view. In the 
stages of figs. 119 to 126 there is no marked change in this layer 
of chromatin, beyond that the area of. interruption opposite the 
centriole becomes reduced. Then the whole nucleus becomes 
smaller, with enlargement of the area of interruption of the 
chromatin (figs. 127-136); this phenomenon is associated with 
discharge of substances from the nucleus and will be described 
in the section on the idiochromosomes. It next begins to elon- 
gate (figs. 184-138). Later (figs. 139, 140) it becomes laterally 
compressed, the peripheral chromatin again extending nearer the 
centriole. Thus the chromatin cylinder lengthens and grows 
bilaterally symmetrical; fig. 141 exhibits it from its flattened 
surface, showing how the border next the perforatorium is more 
arched, while the opposite surface remains more flattened. Figs. 
142 and 148 illustrate two immature sperm of a later stage from 
- one cyst; the first is seen from its flattened surface while the other 
is viewed from its narrow edge; thus the sperm head has grown 
into the shape of a shallow, pointed spoon. At the same time it 
becomes spirally twisted to a slight extent. A later stage, seen 
from the flattened surface, is shown in fig. 144, and a cross sec- 
tion of a head of the same stage in fig.145. The latter figure illus- 
trates how the concavity of the head has become a deep groove 
and it is this longitudinal groove that might mislead one, view- 
ing the head from the side, into supposing that there were an 
axial rod contained within the cylinder of chromatin. In this 
way the sperm head changes from the shape of a bent spoon to 
that of a narrow, pointed rod, with a deep groove on that sur- 
face directed away from the perforatorium. A later condition is 
drawn in fig. 146, and a mature sperm head from the distal end 
of the testis in fig. 147. Seen from its more flattened side the 
mature head shows as a thin hollow cylinder of chromatin con- 
taining a distinct cavity filled with nuclear sap, but seen from its 
