HOYLE: REPORTS ON THE CEPHALOPODA. 53 



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, A 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 in the margin of a scale, which gives passage to the 

 nerve as mentioned above (Fig. 4, B, n). 



The fibrillar structure is not shown in these tangential sections, but there 

 are indications of the presence of lacunae 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, i. c.) might perhaps be more correctly termed a 

 funnel, for where the bottom would be is a space thnnigh 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 ram. 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 ratlier coarse fibres, which pass from the 

 deeper portion to the more superficial, in layers parallel with the inner surface 

 of the 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. viarfjaritifera, in 

 which species, too, there are no nerve channels to be seen, — a fact which is 

 probal)ly 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 (P>) a cone occupying the axis of the organ, and bearing 

 on its apex the knob just mentioned. 



(A) Tlie spheroidal knob (s. k.) occupies the centre of the posterior cup, and 

 constitutes, in fact, a nucleus around wliich the concentric layers of scak'S are 

 arraTiged. It is about 0.1 mm. in diameter. 



(B) Tha axial 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 tlie 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, bas;d diameter, 0.23 mm., 

 apical, 0.00 mm., total length, including the spheroidal knob, 0.21) 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., tliough many are much less. They consist of almost structureless 

 protoplasm, which stains but slightly, and the cell-boundaries jxre indistinct. 



