beyond the pioboscidial epithelium and its contained 

 cavity, and fusing with the muscles of the proboscis 

 sheath. The ninscular slip so formed has been termed 

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

 ful whether it exercises the function which its name 

 implies. Xot only does it appear too slender to exert the 

 necessary foice, l)ut the distance between its point of 

 attachment to the jnolioscis sheath and the ])r<)l)oscis j)ore 

 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 piesent, 

 would seem to indicate that, whilst ex})ulsion is dwo to 

 pressuie exerted on the rhynchoc(elomic fluid ))\- the 

 circular muscles of tlie pidboscis sheath or of the body 

 wall, retraction is prol)ahly accomplished l)y a peristaltic 

 movement of the j)roboscis 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 bioken-oif organ being mistaken for a 

 young worm just born. 



THE AL1MEXT.\KV C.\XAL. 



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 intluence 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 fr(un 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 (esophagus, 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 



