236 WM. A. KEPNER AND J. R. CASH 
either causing great distortion or disintegration of the animals. 
The worms were cut into sections, some three and some five 
micra thick and the sections stained with iron haematoxylin 
and counter stained with Bordeaux red. Macerations stained 
with such intra vitam stains as Wright’s stain and methylen 
blue were very valuable in corroborating results. 
HISTOLOGY, OF. THE: PIT 
The histology of the pit involves an understanding of the 
epidermis. The epidermal cells of the animal have the power 
to secrete a protective mucus-like substance. That such is 
the case can readily be seen by placing the animal in an abnor- 
mal solution of not too rapid killing power. The animal will 
at once enshroud itself in a thick sheath of protective mucus 
within which it swims around. Such a phenomenon will be 
more fully described in a later part of this paper. 
The pit is associated with a region of the central nervous 
system known as the ciliated pit-ganglion. The pit, as well as 
this ganglion, is a modified region of the general epidermis. 
The marginal walls of the pit are formed by cells transitional in 
structure between the general epidermis and the low cells at 
the bottom or fundus of the pit. As the invagination which 
forms the pit takes place this transition takes place until there is 
a layer of low, small epithelial cells lining the fundus of the 
pit. The boundaries of these fundus cells are less pronounced 
than the boundaries of the general epithelial cells and their 
nuclei less frequent. In certain regions of this lining of the 
fundus the few nuclei which are present are indefinitely placed, 
which fact suggests that there is no basement membrane. 
On the exterior of the body, lying close upon the fundus of the 
pit, is a homogeneous mass of mucus-like substance. The mar- 
ginal walls of the pit are thickly covered with cilia which appear 
to be longer than the cilia of the general body epithelium, but 
no cilia at all were found upon the low cells lining the fundus 
nor were any seen projecting above the homogeneous mass of 
mucus-like substance. 
