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each of them of only one cell with the pigmentgrains lying only at 
the periphery, just as Heimans and v. p. Stricut') had said in 1898; 
by BEER *) and ScHNEIDER*) the description given by Hesse was taken 
for right and confirmed. 
As to the arrangement of the pigmentcells in the spinal cord in 
the first place, the observations of Hrssr are not complete. They do 
not simply lessen in number going from before backwards. In 
young pelagic larvae there are to be seen very distinctly two groups 
of pigmentcells, one in the cranial part of the body, the other in 
the caudal half. Between those groups there are much less pigment- 
cells in each segment. In later stages however these two groups 
become fused, and then the arrangement is in the main as it is 
described by Hessr. 
As regards the position occupied by the pigmentcap on the eye- 
cell, I can in the main confirm the observations of Hrssr. The 
eyes at the ventral side of the central canal are always looking 
down, those at the left are mostly looking upwards and to the right, 
those at the right mostly downwards and to the right. 
The histological structure of the eyes seems to me to be slightly 
‘different from the one described by Hesse and SCHNEIDER. 
The nucleus of the pigment-cell is never lying at the concave, but 
mostly at the convex side of the cupshaped cell; sometimes the 
nucleus is found in the middle of the pigment-cell, where often a 
clear pigmentfree zone of protoplasm may be distinguished. According 
to Hesse the pigment-cup consists always of only one cell. Now 
sometimes in young animals, where the pigment is of a light-brown 
colour and the nucleus may therefore be seen very clearly, I found 
two nuclei in the pigment-cap, and so it seems to me that there are 
sometimes two pigment-cells with one eye-cell. So the form of 
the pigment-cap in fig. 3 seems also to point to the pigment-cap 
being composed of two cells. As a rule, however, there is only 
one pigment-cell in each eye. 
In the eye-cell, lying under the pigment-cell, Hesse describes a 
double row of small rods, lying close to the pigment-cell. This 
double row of small rods exists, but the two parts of it are not 
separate, but continuous at both ends, in whatever direction the cell 
is cut through. So a flat oval body is formed, with a striated wall, 
lying close to the pigment-cap (fig. 1.@), and following in its shape 
the form of the cap. This body seems to me to be homologous with 
') Mém. couronn. de |’Acad. roy. de Belgique T. LVI 1898. 
2) Wiener med. Wochenschrift 1900. 
$) Lehrb. der vergl. Histologie der Tiere 1902, 
