266 
SIDNEY F. HARMER. 
amongst the purely epithelial cells. These structures, much 
less numerous than the latter, are in reality ectoderm cells, 
which form the terminations of sensory nerves. Each is a 
nucleated cell of small size, bearing one or more fine, stiff, 
tactile hairs, projecting into the water (fig. 8). 
(iii) Gland Cells. — In certain regions of the body occur 
large unicellular glands opening to the exterior, and presenting 
a considerable amount of variation in the different species. 
Attention was first directed to these structures by Salenskv 
(15), who described them in L. crassicauda and L. Tethyae. 
In silver nitrate preparations of the former they may be seen 
to open between the ordinary epithelial cells by wide aper- 
tures (fig. 7, age), whose margins are surrounded by a thick 
black line : in most cases they occur in a row parallel to the 
edge of the vestibule, and reaching almost to the beginning of 
the stalk. The apertures of the gland-cells are situated just 
on the anterior side of the edge, in the condition of complete 
retraction of the tentacles. In L. crassicauda two very 
distinct forms of gland-cells are present (fig. 8) : the one 
nearly transparent and filled with large spheroidal vacuoles 
(gc. 1 ) ; the other opaque, and composed of a large number of 
small granules (gc. 2 ); the nuclei of the gland-cells can be 
detected in sections. In L. Leptoclini (fig. 2) the gland- 
cells occur only at the sides of the calyx, and differ from those 
of L. crassicauda in possessing a large central vacuole sur- 
rounded by a thin layer of protoplasm, embedded in which is 
the nucleus. Whether the characteristic apical cells of L. 
Leptoclini (fig. 2, ac.) belong to the same category as the 
gland-cells appears doubtful ; it is, perhaps, more probable 
that they belong to the mesoderm, as in section they 
appear to be covered externally and internally by a layer 
of epithelium. The function of these curious cells has not 
been made out ; their position is sufficiently indicated by 
fig. 2. 
In L. Tethyse the gland-cells are very numerous, and closely 
packed together round the ventral end of the vestibule ; they 
are composed of a granular material, which stains with great 
