TOT2: | E. GHosu: The Anatomy of a Slug. 189 
then to the left. In A. leuckarti and A. strubelli, it ends in the 
anterior end of the digestive gland. 
Minute structure (pl. xxv, fig. 10).—The oesophagus consists 
of the following coats from without inwards :— 
(x) A thin layer of connective tissue consisting of a few 
white fibres and elongated fusiform connective 
tissue cells. Just beneath this layer are seen two 
nerves (oval in transverse section) passing along 
the sides of the ventral surface of that portion of 
oesophagus which passes backwards from beneath 
the intercerebral commissure to the digestive gland. 
(2) Alternate layers of longitudinal and _ transverse 
muscle-fibres with loose connective tissue interven- 
ing between them. The fibres do not form con- 
tinuous bundles, but are arranged irregularly. ‘The 
fibres of different layers often communicate with 
one another. The bundles become smaller and 
smaller as we pass inwards. The longitudinal fibres 
become predominant on the inner side and form 
several longitudinal folds, generally nine in number, 
which project into the cavity of the tube. 
(3) The mucous membrane consists of a single layer of 
columnar epithelium. The cells seem to be ciliated. 
(v) The digestive gland, mid-gut gland or liver (pl. xxv, figs. 6 
and 8) is a large elongated conical (or fusiform) body wide and 
rounded in front, but tapering and pointed behind. It occupies 
more than the posterior two-thirds of the body. In front it lies in 
connection with another small gland, the accessory digestive 
gland, and it is connected at its hinder end to the terminal 
body-wall by strands of connective tissue. The outer surface 
of the gland is smooth, but presents some transverse fissures. 
The inner surface is raised into numerous folds and papillae which 
increase the absorbing surface to a greatextent. The wall of 
the gland is thick, and the gland is circular in transverse section. 
In A. strubelli and A. sempert (10), the outer surface of 
the gland is finely lobulated but the inner surface is smooth 
and circular in transverse section. In both the gland is of 
dark colour and is conical in shape. In A. leuckarti (10) the 
gland is irregularly lobed and presents a process to the left from 
near the anterior end. 
Minute structure (pl. xxvi, figs. 14, 15).—The whole gland is 
surrounded by a thin layer of connective tissue (consisting of white 
fibres and connective-tissue cells). This ensheathing layer gives 
off numerous strands which converge and pass inwards to form the 
core of numerous papillae and folds which project into the 
cavity of the gland. These strands consist of connective-tissue 
fibres with a few muscle cells. These strands are surmounted 
by a single layer of cells which are placed side by side without 
any interspace between them. The cells are arranged to form 
