200 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
loose, but the ends of each bundle are gathered up into 
a tendinous root, which penetrates the muscular layers 
of the body-wall, and has its attachment in the fibrous 
connective tissue which is present among the muscle 
fibres. These straight transverse bundles occupy the 
ereater portion of the cavity of the proximal limb. Towards 
the axial portion they separate, leaving a space in which 
the convoluted and straight portions of the intestine 
are lodged. Between them penetrate the tubules of the 
gonads. 
(4) The pallial muscles consist of the retractor muscles 
of the mantle edge and siphons and the intrinsic muscula- 
ture of the siphons. The former (Ret.m., fig. 3) form a 
radial series which extend round the mantle edge from 
adductor to adductor. They are inserted into the shell 
along the pallial line (Ret.m’.; Ret.s’.; fig. 10), and 
extend into the folds in the mantle edge where their 
distribution has already been described. Their length in 
the extended specimen is about 0°5 cm. Towards the 
posterior margin of the shell they become very much 
stronger in correlation with the development of the 
siphons, for the retraction of which they serve. In the 
walls of the siphons they form a dense longitudinal sheath 
which extends outwards to the tips. This sheath lies 
principally on the imner portion of the wall. Special 
circular and radial intrinsic fibres are present in the 
siphonal walls. The former are distributed in bundles 
lying just beneath the outer wall, and less evident bundles 
situated midway between outer and inner walls. The 
radial fibres pass across from inner to outer epidermis. 
The outer zone of the siphonal wall consists of connective 
tissue with included blood spaces. 
