442 IRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
however, on the ground of structure, the nucleus, and the 
failure to prove a connection with nerve fibres, considers 
them to be supporting cells. Until the difficulties of 
following their fine fibrils are overcome, it will be better 
to call them interstitial cells, which leaves the question 
of function open. 
Argentea —Underlying the retina is this layer (fig. 
29, Arg., fig. 34), made up of refractive granules. This 
is the layer which gives the eye the beautiful metallic 
appearance, aided, of course, by the pigment layer—the 
tapetum. Patten, by painting several white lines on the 
base of the objective and focussing down on a large eye 
removed from the mantle, was able to see the image 
formed in the eye. ‘The different layers could be followed, 
and the image was seen to be most distinct just before 
reaching the tapetum and argentea, so that the lens and 
argentea together act as a true optic lens and murror, 
and form an image just where the rods are placed to 
recelve it. 
The argentea (which does not generally stain in 
sections), is made up of several laminae, and longitudinal 
sections have the appearance of a series of layers of small 
iridescent scales. If the argentea be looked at from the 
surface (fig. 34), it 1s seen that the layers are formed of 
numerous very small and almost square plates. These 
are arranged regularly together in one plane, so that the 
square face of each plate is in the plane of the argentea, 
and the edges only are seen in longitudinal sections. The 
argentea is thickest in the centre, where the laminae are 
most numerous, and towards the sides it thins out. There 
are no nuclei in this layer. 
Tapetum.— Below the argentea is this red pigment 
layer (fig. 29, Tap.). It is of considerable thickness in 
the centre, but, like the argentea, decreases towards the 
