138 JOURNAL OF ENTOMOLOGY AND ZOOLOGY 
through the connective tissue. The lining of the body cavity is 
thinnest over the back (10 microns), thickest over the side (30-40 
microns) and slightly thinner over the foot than over the sides, 
but here it is strengthened by additional fibres in the connective 
tissue. These form a layer just above the glandular part of the 
foot, as well as an interlacing network of fibres. Fibres also 
branch off from the lining layer at the sides, above and below, 
and run diagonally towards the mantle edge, towards the outer 
angle of the foot, and into the papille. 
The papille are club-shaped processes, coming off from the 
mantle edge in groups of various sizes. They are covered with 
an epithelium similar to that covering the rest of the body and 
contain a large branch of the mantle nerve, a large blood sinus, 
a core of spicules, and a gland. The sinus extends along the 
dorsal side of the papilla. At first it has a distinct wall, but the 
upper portion breaks up into branches which communicate with 
interstices in the very spongy connective tissue of which the body 
of the papilla is composed. The nerve lies just ventral to the 
sinus. It gives off many branches in its course and finally ter- 
minates in the gland at the tip of the papilla. The core of 
spicules extends from the base of the papilla for about two- 
thirds of the distance to the tip, on the ventral side. It is sur- 
rounded by a layer of circular muscle fibres and receives the 
fibres spoken of above as coming off diagonally from the mus- 
cular layer of the body wall. The gland of the papilla is situated 
at the tip. It consists of a spherical mass of cells enclosed in a 
heavy wall, and opening by a short duct surrounded by a thick 
mass of circular muscle fibres. Nearly all of the cells of these 
glands were empty in the preparations, probably because the 
animal discharged the secretion when it was killed, but a few 
contained large, dark-staining granules in a lighter, alveolar 
mass. These full cells were pear-shaped, the nucleus being situ- 
ated at the base at the smaller end, and the cells were apparently 
attached to the basement membrane by long, slender processes. 
As the whole structure of the gland would indicate that it is 
intended to forcibly eject the secretion, it seems likely that it is 
used as an instrument of defense. 
