1915.] E. GHosH: The Anatomy of a Burmese Slug. 155 
the morphologically inner surface of the posterior portion of the 
sheath now becomes external and lies in contact with the inner 
surface of the anterior portion. On the dorsal surface and the 
lateral aspects of the anterior portion of the proboscis sheath 
are numerous flattened muscular strands which pass upwards 
and backwards to be inserted into the thin dorsal integument. 
The presence of these strands prevents this tubular anterior 
portion of the proboscis sheath from being protruded with the 
proboscis. Again the posterior division of the sheath, which, 
owing to the doubling of its wall, is placed inside the anterior 
division, is prevented from being straightened out behind by 
the presence of fine strands of connective tissue, which extend 
from its morphologically outer side (inner side in the present 
condition) to the outer surface of the proboscis in a direction 
backwards and inwards from the wall of the sheath. 
It is remarkable to note that in A. (P.) kempit, Ghosh, 
owing to the absence of special muscle strands from the outer 
surface of the proboscis sheath to the dorsal integument, the 
proboscis can be extended to its full extent so that the wall of 
the sheath is seen to become continuous with the anterior end 
of the head in the position of the mouth. A partial protrusion 
of the proboscis is only possible in the present case. Again a 
simpler condition exists in A. (P.) sanguinolenta (Stol. MS.). 
Here the proboscis is attached behind to the posterior end of 
the sheath surrounding it, just in front of the beginning of the 
oesophagus, so that after the proboscis has been fully protruded 
it drags from behind the sheath which then becomes gradually 
everted and forms a covering of the radular portion of the 
proboscis, so that the proboscis sheath becomes continuous with 
the proboscis in front. 
Hence the present species shows an intermediate condition 
as regards the structure of its protrudable buccal bulb. 
Minute structure of the proboscis.—The inner surface is raised 
into transverse folds; the ridges on the upper half fit into 
depressions on the lower half like the teeth on the blades of a 
pair of forceps. The inner surface of the organ is lined by 
a single layer of cubical epithelium which secretes a layer of 
hard homogenous cuticle,.as thick as the cells themselves. On 
the outer side of the epithelium are placed the muscular layer, 
the bundles being arranged in various directions. 
(ii) The vadula sac is a club-shaped body curved somewhat 
like the letter S, the narrow end of which is attached to the 
posterior end of the proboscis. The sac is surrounded by a thin 
outer coat of muscular tissue within which is a thick muscular 
coat. Both these two coats are continued behind to form the 
retractor muscle. Beneath the thick inner coat and lying in 
the ventral and lateral aspect of the cavity of the sac, is a thick 
flap of muscular tissue which is attached to the inner surface of the 
muscular sheath behind and laterally, but projects anteriorly into 
the cavity about half the length of the sac from its posterior 
