80. THE ANATOMY OF AN AUSTRALIAN LAND PLANARIAN. 
not confined to any one region of the body, but make their appearance more or less 
sporadically, although naturally chiefly at the anterior end, which, it will be 
remembered, is uplifted and constantly moving about when the animal crawls. 
I have pointed out, on a previous page, that the groups of rod-like bodies 
originate each in a single cell, and that the rods appear as small streaks around the 
nucleus, which afterwards, as the mother cell passes outwards, increase in size and 
numbers, so as ultimately completely to conceal the original cell and nucleus, and then 
separate at their outer ends. I believe that each eye is probably merely a special 
modification of a group of rod-like bodies and their mother cell, the segments of which 
the pigment cup is formed being homologous with the rods and the nucleated lens 
representing the original mother cell. ‘To obtain such an eye from a group of rod-like 
bodies we have only to imagine the original mother cell increasing in size instead of 
dwindling away, and the rods developing around the outside of the cell only, in fewer 
numbers and of larger size. The eye is, itis true, considerably larger than an ordinary 
eroup of rod-like bodies, being about twice the size, but there is no reason why growth 
should not continue beyond the ordinary limit if the mother cell retains, as seems 
probable, its activity for a slightly longer period than usual. The colour of the pigment in 
the eyes and its deposition in definite granules is perhaps a more serious objection, but 
cannot, I think, be held to invalidate the theory. The colour of different species of 
land Planarians varies enormously, and probably (though this remains to be proved) 
the pigment in differently coloured species will be found to be lodged in the rods, as 
in Geoplana spencert. If different colours may be developed in the rods in different 
species there is no reason why the rods of any one species may not differ in colour. 
So far as can be judged from Moseley’s account (6) the eyes of Bipalium agree very 
closely in structure with those of Geoplana spenceri. Moseley states that the eye is a 
simple sac or cell, the anterior part transparent and lens-like, the posterior and larger 
portion darker and opaque, owing to the presence of brown pigment granules imbedded 
thickly i its wall. An unpigmented dot often present in the posterior part seems to 
show that the eye spots are modifications of single nucleated cells. In the interior of 
the eye spots a lens-like body is visible in sections, but very little differentiated from 
the general cell contents, and hard to see. Between the lens-like body and the 
interior of the pigmented back of the eye spot is a highly refracting substance. The 
position of the eyes in Bipalium also agrees with that in Geoplana. In Geoplana I can 
detect, however, no “highly refracting substance,” and the position of the nucleus 
(if the structure described by Moseley be a nucleus) is also different. Still the 
fundamental agreement of the eyes in the two cases is obvious. 
Amongst land Planarians we meet with two very different types of eyes, which we 
may call the unicellular and the multicellular. The unicellular eyes are met with, for 
