THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 79 
I.—The Eyes.—The only special sense organs which I haye found in Geoplana 
spencert are the eyes. ‘These are very abundantly present as numerous minute black 
specks placed ventro-laterally, in an elongated patch at each side of the extreme 
anterior end, and extending all round the horseshoe-shaped anterior margin. In the 
living worm the eyes are a good deal obscured by the dark pigment of the body. 
The eyes are not absolutely confined to the front end of the body, for I have found a 
few at the extreme hinder extremity, recalling the condition described by Moseley (6) 
in Bipalium, where the eye-spots are numerous at the anterior end, and also sparingly 
present over the entire length of the body to the very tail. In Geoplana spencer, 
however, I have only found eyes at the two extremities, but in Geoplana traversi 
Moseley (1) records the fact that eye-spots are scattered more sparsely on the lateral 
margins of the body, along its entire length posterior to the principal patches. 
The position of the eyes with regard to the different layers of the body is shown in 
figures 10 and 11. They are placed just outside the special zone of rod-lke bodies 
along the line where the latter begin to thin out towards the ventral surface, and 
they lie unbedded in the nerve sheath. 
The structure of the eyes is very simple. In longitudinal section (Fig. 25) the 
outline of the whole eye is more or less elliptical, the longer axis of the ellipse, which 
measures about 0°06 mm., being placed at right angles to the surface of the animal. 
The eye consists of two parts—(a) a pigment cup, (0) a lens (vide Figs. 25, 26). 
The pigment cup is widely open at its outer end and surrounds the lower two-thirds 
of the lens. It does not form a perfectly continuons layer around the lens, but is 
made up of some four or five elongated segments, which meet at their edges and call 
to mind the petals of a flower. The divisions between the segments are most obvious 
at the margin of the cup, but can be traced right down to the bottom. ‘The pigment — 
is deposited in the segments of the cup in the form of very minute, closely packed, 
splerical granules, of a brown colour. The lens is a somewhat elongated, faintly 
staining, very slightly granular body lying in the pigment cup. Its outer extremity 
projects for a short distance beyond the margin of the pigment cup, and presents a 
convex, almost hemispherical surface towards the outside of the animal. At its inner, 
- somewhat narrower end, the lens contains a nucleus (Fig. 26, 7). Between the lens 
and the pigment cup, and also just in front of the outer surface of the lens, small 
spaces are visible, doubtless caused by shrinkage of the tissues. 
The eyes of Geoplana spenceri appear to be unicellular bodies, and their position 
and structure suggest what seems to me a very probable theory as to their origin. 
They lie always immediately outside the special zone of rod-like bodies, and they are 
