Habits and structure of Cotylaspis insignis Lerpy. 219 
it was found in 52 cases that both were present in 29 individuals, 
both were absent in 12 cases, the left one only was present in 8 
and the right only in 3 cases. In some cases where the eyes, one 
or both are absent, scattered grains of pigment found in that part 
of the body are evidence of its recent degeneration and disappearance. 
The eyes are placed (see Fig. 30,31) upon the inner surface of the 
lateral nerve just posterior to its connection with the transverse 
commissure. The eye is a hollow cup of pigment consisting of 
minute dark-brown grains imbedded in a granular medium, the mass 
so shaped as to be thicker at the base and to thin out on the rim, 
the base is in connection with a nucleus, thus conforming with the 
type of eye found in the flat-worms generally (Hesse, 1897). The 
interior of the cup is occupied with a non-stainible granular material 
which abuts directly upon the the fibrous material of the nerve 
trunk (Fig. 31). None of my sections will bear the interpretation 
that this granular material is a “visual cell” functionally developed, 
as found in the monogenetic trematodes (e. g. Zristomum, HESSE, 
1898, fig. 29) and in the turbellarians: a nucleus so noticible in 
them cannot be found in my sections, the fibrillar structure and 
beginning of the nerve fibres is not shown and the striated band 
on the border of the cell in connection with the pigment cell is not 
present. Since the histological structures in the animal in general 
are fairly well preserved and the plane of the section is favorable 
to showing these structures, if present, I am forced to conclude that 
the visual cell is not present though the pigment cell is so well 
developed, and that the eye is not functional. They would then 
seem most likely to be merely vestigial structures. They are very 
transitory structures as they do not appear till late ontogenetically 
and disappear before the animal has reached old age. Eyes do not 
occur elsewhere among the Aspidobothridae so far as at present 
known. 
Certain organs are found in the outer portion of the cuticle, 
which may be tactile in function. Their location can be seen by 
reference to Fig. 32, a view from a tangential section of the surface 
and their structure from Fig. 33 which is vertical to the surface. 
They are irregular in arrangement and more numerous at the anterior 
end of the body. The organ sometimes occupies a low conical ele- 
vation of the cuticle. It is located in the outer half of the cuticle, 
and a thread from it runs down through the cuticle and is lost in 
the tissues beneath. The organ measures 0.0035 mm in length and 
