HOYLE: REPORTS ON THE CEPHALOPODA. 09 
naturally give the best idea of it, but even here it is impossible to be certain 
that in any particular case the whole outline is shown, Two scales from the 
same series of sections are shown in Fig. 4, 4 and B. 
Comparison of a number of such sections leads, however, to the belief that 
they are, speaking generally, oblong in form with rounded angles. Here and 
there a deep notch is seen iu the margin of a scale, which gives passage to the 
nerve as mentioned above (Fig. 4, D, n). 
The fibrillar structure is not shown in these tangential sections, but there 
are indieations of the presence of laeunae which may, perhaps, be the inter- 
spaces between them. There are great variations in the constitution of the 
scales in the different sections, which I can only attribute to the state of 
preservation. 
As compared with P. margaritifera, the scales are less regular in arrange- 
ment and not so homogeneous in structure. 
3. The Inner Cup (Fig. 2,2. c.) might perhaps be more correctly termed a 
funnel, for where the bottom would be is a space through which passes the 
central mass to be described below, and not only is the diameter of the cup 
much larger at the top, but the thickness, too, increases very greatly towards 
What may be termed the rim, whilst at the bottom it tapers away to a thin 
edge. The internal diameter of the cup at the mouth is 0.2 mm. and at the 
bottom 0.09 mm., the depth 0.12 mm., and the thickness of the rim about 
0.08 mm. It is composed of a mass of rather coarse fibres, which pass from the 
deeper portion to the more superficial, in layers parallel with the inner surface 
ofthe cup. Here and there an opening is left through the wall of the cup, 
apparently for the passage of a nerve. The fibres are much coarser and more 
closely packed, and stain much more deeply than those of P. margariti 
which species, too, there are no nerve channels to be seen, —a fact which is 
probably to be explained by the difference in size and arrangement of the 
central mass in the two species, 
4. The Central Mass may be considered as divisible into two portions: (A) a 
spheroidal knob, and (B) a cone occupying the axis of the organ, and bearing 
on its apex the knob just mentioned. 
(A) The spheroidal knob (s. k.) occupies the centre of the posterior cup, and 
constitutes, in fact, a nucleus around which the concentric layers of scales are 
arranged. It is about 0,1 mm. in diameter. 
(B) The aval cone (a. co.) is situated in the centre of the inner cup. It 
projects through the bottom of the cup to join the spheroidal knob just 
described, and its length being greater than the depth of the cup, it projects 
Some distance above it. Its sloping sides bulge outward somewhat, and its 
upper surface is convex. Its measurements are, basal diameter, 0.23 mm., 
apical, 0.09 mm., total length, including the spheroidal knob, 0.29 mm. 
The bulk of this central mass is composed of large rounded parenchymatous 
cells, closely packed together, They may attain a diameter of as much as 
0.02 mm., though many are much less. They consist of almost structureless 
protoplasm, which stains but slightly, and the cell-boundaries are indistinct. 
