480 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
distributed, but are most numerous and extend nearest to 
the base of the eye stalk, on the upper side which is — 
turned towards the hght (fig. 29, on left side). 
The name iris has been given (fig. 29, 7.) to the zone 
bounding the cornea where most pigment is present. The 
cells of the iris become rapidly less tall, the nucleus 
becomes more central, and then suddenly all pigment 
is lost, and they pass into the cubical, transparent cells of 
the cornea (fig. 29, Cor.). A thin layer of cuticle covers 
the epithelial cells of the eye stalk, the iris and the cornea. 
The function of the iris seems to be, like that of the 
pigmented sides of the eye vesicle and stalk, to prevent 
lateral rays of light penetrating to the retina. 
The cells of the cornea were discovered by Patten (35) 
to be pentagonal or hexagonal in surface view, hour-glass 
shaped in section, quite free from pigment, and to have a 
curious interlocking or notched appearance on the edges, 
so as to give the cornea a much firmer and more rigid 
structure asa membrane. This appearance was described 
by Schreiner (37) as being due to intercellular substance 
and to fixation alone. 
From transverse and longitudinal sections through 
these cells fixed in Mann’s Fluid, Flemming’s Reagent 
and Osmic Acid, I am of opinion that they do possess 
processes on all sides which probably connect them 
together, as in the so-called “ Prickle Epithelium.” This 
occurs also in the epidermal cells of the eye stalk (fig. 35). 
The connective tissue which makes up the rest of the 
eye stalk is a continuation of the same from the mantle, 
and is similar in structure. There are numerous lacunae 
with blood corpuscles, and the rest consists of 
almost structureless, homogeneous connective tissue with 
scattered nuclei and a few muscle fibres (fig. 29, Op. m.), 
which later are present in considerable quantity in the 
