248 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



beyond the proboscidial epithelium and its contained 

 cavity, and fusing with the muscles of the proboscis 

 sheath. The muscular slip so formed has been termed 

 the retractor muscle of the proboscis, though it is doubt- 

 ful whether it exercises the function which its name 

 implies. Not only does it appear too slender to exert the 

 necessary force, but the distance between its point of 

 attachment to the proboscis sheath and the proboscis pore 

 is considerably less than the length of the proboscis. 

 Such considerations, coupled with the fact that in some 

 nearly allied species no retractor muscle is present, 

 would seem to indicate that, whilst expulsion is due to 

 pressure exerted on the rhynchoccelomic fluid by the 

 circular muscles of the proboscis sheath or of the body 

 wall, retraction is probably accomplished by a peristaltic 

 movement of the proboscis itself. Such a form of move- 

 ment may be observed in the isolated proboscis, and once 

 gave rise to the view that these worms were viviparous — 

 the extruded and broken-off organ being mistaken for a 

 young worm just born. 



THE ALIMENTARY CANAL. 



The mouth in the living and active animal is an 

 elongated slit on the ventral surface just behind the brain. 

 When widely open under the influence of a narcotic it 

 becomes circular in outline, and surrounded by a promi- 

 nent and somewhat rugose lip. In life apparently one of 

 its functions is to act as a sucker, since, when the animal 

 is forcibly removed from the surface on which it rests by 

 a current of water from a pipette, the mouth area retains 

 its attachment more vigorously than the rest of the body. 



The oesophagus, into which the mouth leads, is thrown 

 into a number of longitudinal furrows, which largely 

 increase its surface (PI. II., figs. 1 and 2). It has been 



