62 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
section (Fig. 4) it is marked by striations which run, roughly speaking, par- 
allel to its outer boundary and seem to indicate that it is built up of irreg- 
ular rods packed closely side by side, A fair number of more or less complete 
axial sections of this structure have been obtained, but I have only been 
able to discover one or two fragmentary transverse sections. These show the 
cut ends of the rods packed together with a kind of radiating arrangement 
from the central aperture towards the circumference (Fig. 7). Between these 
rods, nuclei occur very sparingly and elongated in a direction parallel with 
the rods themselves. 
4. The Posterior Hemisphere (Figs. 4, 8, p. h.) occupies the deepest portion 
of the interior of the organ just within the pigment cup. It has, roughly 
speaking, the form of a hemispherical bowl with the rim turned inwards. Its 
thickness is about equal to one-third of its diameter and is such that only a 
very small spheroidal space is left in the middle of it and is occupied by the 
end of the internal cone. The thickness js made up of a series of concentric 
layers which in the sections appear to be slightly separated one from the other, 
especially near their edges, but this may be an effect produced by the process 
of cutting. This substance takes up the stain only faintly, and appears to be 
somewhat denser in consistency than the inner cup. No nuclei have been 
noticed anywhere in its substance. 
5. The Internal Cone (Figs. 4, 6, 7, 4. co.) is situated with its base against the 
deeper surface of the lens, whilst its spheroidal apex occupies the internal cavity 
of the posterior hemisphere just described. It is deeply subulate and is bounded 
by the internal surface of the inner cup. Under a high power it is seen to be 
composed of finely granular protoplasm, which is not much affected by the 
staining fluid. No definite cell boundaries can be seen, but it contains a con- 
siderable number of nuclei. Those near the base of the cone are small and 
ovoid in shape, whilst the deeper ones are elongated in the direction at 
right angles to the axis. Some of them are so long as to occupy a con- 
siderable portion of the diameter of the cone. A section parallel with the 
surface of the integument (Fig. 6) just beneath the lens shows that these 
elongated nuclei have their long axes curved to correspond with a circle 
drawn round the centre of the cone. They are situated in the deeper 
layers, whilst the round and ovate nuclei occupy the circumference. 
I have not been able to trace the nerve supply to these organs. 
IL SUB-OCULAR ORGANS. 
Beneath each eyeball, covered in the living condition by the integument, is a 
row of five organs, placed at equal distances from each other along the equator 
of the ball (Plate 10, Fig. 2). They are visible in the living animal (Plate 1, 
Fig. 9) evidently by reason of the transparenoy of the integument. 
They are slightly elevated papillae of a clear yellowish-brown color. The 
three central ones are the smallest and are about 0.18 mm. in diameter, 
