270 E. A. ANDREWS 
photograph (fig. v) but present one of their canals in the shell of fig. 
23, to the right. In contrast to the excessive thickness of the shell 
of this main stem of the endopodite, the triangle, as repre- 
sented by the lower part of this section, is relatively thin shelled. 
The radius is the thick knob in the lower left corner. The shell 
to the right is the ulna, the thick mass against the concavity of the 
triangle is in reality more membranous than calcified, but as yet 
thick. But further toward the elbow (fig. 24) along the line 24, 
(fig. 22), the corresponding region is a thin membrane reaching 
from the neck of the radius across to the thick guide ridge. In 
reality the elbow stands out more as in fig. vir so that the width 
of the section 24 is much greater than fig. 28. Fig. 24 shows 
clearly, on the right, the hinge-like line of demarcation between 
the outstanding triangle and the main stem of the endopodite, 
being in fact cut at the edge of the proximal articulation of the hum- 
erus (fig. vr), where there is a sudden change in level in passing from 
the humerus to the main stem. In sections 23 and 24, the small 
black dots above within the connective tissue, are the muscles 
that run up into the flagellum, much as in fig. 28. 
Section 8 shows the radius standing out from the flat triangle 
with the thick mass of the humerus above in the figure, while 
fig. 9 shows the thick end of the endopodite above and in the 
groove of the first stylet the cut off wedge, as will be described 
below in considering the adjustments of the first and second stylets 
during conjugation. 
ONTOGENY OF THE ACCESSORY, OR SECOND, STYLET 
Between the individual development of the first and the second 
stylets there is this important difference that while the first never 
at any time looks like one of the ordinary pleopods but is of late 
appearance and is also a dwarfed, specialized, or reduced append- 
age from the first, the second appendage is present as soon as the 
others are and is at first like the ordinary appendage and becomes 
specialized by the addition of an outgrowth and not by the loss 
of parts. 
