DR. ARTHUR FARRE ON THE ORGAN OF HEARING IN CRUSTACEA. 241 
Fig. 2. Portions of the lesser or first pair of antennae viewed from above, showing the 
fenestra ovalis and membrane covering it ( b ). 
Fig. 3. Right antenna. A bristle is passed into the aperture which leads to the inte- 
rior of the sac. The valvular portion is seen at a. 
Fig. 4. The fenestra ovalis, with its membrane and a portion of the surrounding sub- 
stance, have been removed, showing the vestibular sac immediately beneath. 
The surrounding flesh has also been removed. In this figure the aperture 
at the inner and upper angle is more distinctly seen ( b ). 
Fig. 5. Upper portion of the vestibular sac removed, showing the interior of the 
cavity, with the crescentic arrangement of ciliated processes and grains of 
sand at the bottom. 
Fig. 6. The same part removed, and the grains of sand washed out and lying by the 
side to give a clearer view of the interior. 
Fig. 7- The same, showing the arrangement and form of the ciliated processes, both 
in the centre of the sac b, and at the orifice a. A few particles of sand are 
lying close to the hairs, the rest having been removed. 
Fig. 8. Separate processes from the central row. The processes are covered with fine 
hairs, and some are bifid at their extremity. They contain granules of 
nervous matter. The processes are inflated at their base, where they are 
set on to corresponding apertures in the walls of the sac. 
Fig. 9. Small processes covering other portions of the sac. 
Fig. 10. View of the nervous system (the viscera having been removed) seen from 
below. 
a. Supra-oesophageal ganglion. 
b b. Nerves to first pair of antennse. 
c c. Acoustic nerves. 
d d. Nerves to second pair of antennse. 
e e. Nerves to organ at its base (olfactory?). 
ff. Nervous collar surrounding oesophagus. 
The optic nerve being deep-seated is not shown in this figure. 
Fig. 11. The organ situated at the base of the great antennse. A section has been 
made through the centre, perpendicularly. 
a. Shell, b. Membrane covering the circular aperture and having a bristle 
passed through the opening in its centre, c. Fleshy lining of shell, d. Nerve. 
(All the figures in this Plate are from the Lobster.) 
PLATE X. 
Fig. 1 to 10 from Pagurus streblonyx. 
Fig. 1. Right antenna, upper surface. 
Fig. 2. Right antenna, under surface. 
Fig. 3 and 4. The same enlarged. The valve is seen at a, fig. 3. 
