HOYLE: KEPOKTS on the CEPHALOrODA. 61 



In general, too, tlie deeper half is a little more pointed than the more super- 

 ficial, so that the form of the organ approaches that of a peg-top (Fig. 4). 

 Each oi-gan consists of the following parts : — 



1. The Lens. 



2. The Pigment Cup. 



3. The Inner Cup. 



4. The Posterior Hemisphere. 



5. The Internal Cone. 



1. The Lens (Plate 10, Figs. 4,5, 1) consists of a pale structureless material 

 which is not acted upon by staining fluids. It is divided up by faint irregular 

 lines of demarcation and occasional cleavage gaps into more or less rounded 

 masses, in the interstices between which nuclei are found here and there. 



Vieweel in a section taken along the axis (Fig. 4) the lens is seen to be sep- 

 arated by an ef[uati)rial groove into an inner and outer portion. These differ 

 somewhat in their structure. In the deeper portion, the pieces of which the 

 lens is built up are rounder and more irregular, their depth being not infre- 

 quently equal to their transverse diameter. In the more superficial portion, 

 these pieces are more flattened and taper to their edges on either side, and are 

 fitted into each other something like flattened epithelial cells near the surface 

 of the epidermis. The nuclei are modified in accordance with the tissue in 

 whicli tliey are found, being rounded or sub-polygonal in the deeper portion 

 and flattened in the superficial. The groove above mentioned receives the 

 iuturned edge of the pigment cup. 



2. The Pigment Cup (Figs. 4, 6, 7, 8, p. c.) is in the shape of a goblet without 

 a stem and with the edge somewhat inverted. It is built up of a number of 

 sejiarate pigment masses which are seen in section to be hollow Siics with a 

 thick lining of black pigment, a structure which suggests the view that thev 

 are possibly modified chromatophores. Their boundaries are not always 

 visible, and hence it is impossible to determine their exact number, the more 

 so as the sections of the posterior part of the organ are never entire. In a 

 horizontal section taken just below the lens (Fig. 6) there are usually six of 

 these which make up a more or less complete ring, and in such cases the 

 boundaries of the individual sacs are pretty easy to determine. This riu'^ 

 api)ears to correspond to the inturned edge of the pigment cup. In the 

 deeper portions tlie hollow cavities of the jiigment masses are not so easily 

 seen, nor are the boundaries so distinct. The aperture of the cup, as above 

 stated, is occupied by the lens. In its bottom is situated the posterior hemi- 

 sphere, whilst the remainder is lined by connective tissue with numerous 

 large nuclei (Figs. 4, 7, 8, c. t) 



3. IVw. Inner Cup (Figs. 4, 7, i. c.) lies inside the pigim-nt cup just described. 

 It niiglit perliaps be more correctly described as a funnel, for a coni&U perfora- 

 tion runs right through its middle, diminishing in diameter as it descends. 

 The substance of which it is composed stains only very faintly. In an axial 



