90 
Wisconsin Academy of Sciences , Arts and Letters. 
[Fig. 3.] The karyochylema of these nuclei is colorless and shows no granu¬ 
lation. Through it are spread what under a low power appear to be dis¬ 
tinct but isolated masses of chromatin. 
Under a power of about 900 diameters the prismatic cells exhibit more 
of their true structure. The protoplasmic reticulum of the cytoplasm is 
indistinctly seen, most of its exceedingly delicate threads running parallel 
with the long diameter of the cells and presenting the appearance of fine 
striation. The parallel arrangement in this direction may be due to 
the tension of the protoplasm during the rapid centripetal growth of the 
cells. The nodes of the cytoplasmic reticulum are what appear as fine 
granules under a low power. The vacuoles are colorless and are probably 
only drop-like accumulations of cytochylema. In the nucleus the karyo- 
chylema is perfectly colorless and through it runs a net-work of chromatin 
which appears to have thickened nodes. A nucleolus, which stains but very 
slightly, usually occupies a central position. By focussing the distribution 
of the chromatic reticulum is distinctly seen to be peripheral and not sus¬ 
pended in the karyochylema. When only the equatorial plane of the nu¬ 
cleus is in focus the thick masses of chromatin are seen to be closely applied 
to the wall of the nucleus — only a few of them running out into the limpid 
karyochylema. The thin strands of chromatin connecting the irregular 
masses probably also run along the inner face of the nuculear wall. Fig. 5 
represents five nuclei drawn with the focus on their equatorial planes. In 
the interior of the karyochylema the nuceoli stand out distinctly as bodies 
which stain much less deeply than the mass of chromatin. 
The nuclei retain their characteristic structure apparently without the 
slightest alteration till the complete dissolution of the appendage on 
about the twenty-seventh day of development. When at that time the 
nuclei cease to stain, the chromatin [probably now of modified mole¬ 
cular structure] is still visible in glistening masses distributed as formerly. 
The nucleolus, too, is still seen as a less refractive body of greater dimensions 
than any of the irregular chromatin masses. 
The cells of the lower part of tlie appendage in embryos fourteen days 
old [Fig. 3], do not differ in form from the ectoderm cells in general. 
They lengthen somewhat and clasp the inner ends of the large prismatic 
cells which form the great mass of the now nearly solid pleuropodium. 
These smaller ectoderm cells thus form a broad tubular peduncle, the lumen 
of which is in free communication with the body cavity of the embryo. 
The next changes which may be 'noticed in the appendages [in embryos 
about nineteen days old] are superficial and easily described. The tubular 
peduncle increases in length with a resulting decrease in the breadth of its 
lumen. At the same time the portion of the segment to which the append¬ 
age is attached is carried upward and comes to lie somewhat dorsad to 
what will be the coxa of the metathoracic leg. While this movement is 
taking place a constriction appears [Fig. 6 cn.] dividing the bulbous mass 
of large prismatic cells into two segments. This constriction is merely su- 
