JOHNSTON’S ORGAN 31 
_ “This part of the organ contains only such cells and nerve-fibers as are found 
in the ganglion of every sense-organ composed of several elements, and in this 
case they are, moreover, very similar to the elements of the optic ganglion of the 
same animal. Its cells show the same size and also appear to stand in connection 
with each other by a net-work of protoplasmic fibers. 
“ More differentiated are the end-organs proper which form the remainder of 
the nerve-elements filling the interior of the chitinous capsule (fig. 1, St; 4, St). 
These lie inward from the layer of fibers and consist of a great number of small, 
thin, rod-like structures which can only be distinguished clearly in an isolated 
state, after maceration. Such a rod (fig. 5) is 0.04 to 0.05 mm. long, 0.002 to 
0.003 mm. in diameter at its base, and represents a very pointed cone on the sides 
of which are generally found two oval nuclei, 0.005 to 0.008 mm. long and rich 
in chromatin, of which one is situated basally and the other towards the apex. 
In transverse section (fig. 6) the nucleus lies, perhaps covered by a thin layer of 
protoplasm, upon the surface of the rod, which is clasped more or less by it. 
At its base the rod gradually passes over into a fiber which proceeds through the 
fibrous layer to the ganglion cells (fig. 5, F). The body of the rod itself behaves 
towards stains like a cell-body but appears to be of more solid consistence and in 
preparations by maceration often shows an inclination to split from the apex 
into two or three fibres. Ontogeny proves that the rods are formed from the 
cell bodies. The rods are attached or hang by their apices from the chitinous 
processes of the above described central plate (fig. 1, 4), and mostly upon their 
posterior surface. Asis proved by maceration, this connection is a very firm one, 
for sometimes the apices of the rods may still be seen upon the processes while 
the larger part of them is already torn away. Through their slender form and 
close disposition the radiate arrangement is brought about. In longitudinal 
section (fig. 1, St) they correspond approximately with the radii of a circle the 
center of which is situated somewhat before the chitinous process. In a trans- 
verse section through the anterior end of the processes one sees that the rods (fig. 
4, St) are divided into groups corresponding with them ; between these groups 
there are narrow spaces, through about half their length (fig. 4, V), which are 
probably filled with blood during life. In each group the rods lie close together, 
and each, in transverse section, possesses several rods. Upon the rods lying next 
to the interspaces the nuclei are nearer to the apices of the rods than in the 
others ; these nuclei lie upon the surface of the group and bound the interspaces, 
so, that, in a transverse section through the groups striking the rods at about 
their middle, one sees the rods and their nuclei as alternating layers; a double 
layer of nuclei separated by a narrow interspace and a multiple layer of rod- 
bodies, ete. In their basal portion the groups can no longer be distinguished 
fig. 4). 
a. antennal nerve arises on both sides from the anterior ventral part of 
the cerebral ganglion as a large nerve trunk containing ganglion cells. At the 
point of entrance into the antenna the nerve is nearly 0.1 mm. in diameter (fig. 
1, V). After its entrance into the second segment the nerve spreads out in all 
directions and gives off fibers (fig. 1, N’) to the ganglion layer in the entire 
circumference of the organ, and these form a funnel, as it were, upon which the 
nervous parts of the sense organ are attached. These fibers pass through the 
layer of ganglion cells and continue into the fibrous layer (fig. 1, F), which in 
the anterior part of the organ separates the ganglion cells from the rods. This 
funnel is incompletely separated into bundles of fibres by interspersed ganglion 
cells. Other fibers go directly towards the posterior part of the layer of ganglion 
cells and from the center of the funnel there arise two thin threads of fibers 
which pass anteriorly through the opening in the central plate into the shaft of 
the antenna (fig. 1, NV”). 
