23 



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 

 greater 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 (Bet.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 (Bet.m'.; Bet.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 inner portion of the wall. Special 

 circular and radial intrinsic fibres are present in the 

 siphonal walls. The former are distributed in bundles 

 tying 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. 



