v PHYLUM PLATYHELMINTHES US 



4. THE NEMERTINEA 



The Nemerteans are non-parasitic, unsegmented worms, 

 most of which are marine, only a few forms living on land 

 or in fresh-water. They are commonly looked upon as 

 nearly related to the Turbellaria, and were formerly 

 included in that class ; but in some respects they are higher 

 in organisation than the Turbellaria, and they exhibit 

 certain special features distinguishing them from the rest of 

 the lower Worms. 



The body (Figs. 73 and 74) is narrow and elongated, 

 cylindrical or depressed, unsegmented, and devoid of 

 appendages. In length it varies from a few millimetres to 

 as much as ten metres. The entire surface is covered with 

 vibratile cilia. 



The month (;;/.) is at, or near, the anterior extremity, on 

 the ventral aspect. Close above it there is an opening 

 through which can be protruded a very long muscular organ, 

 ti\e proboscis (pr.\ the possession of which is one of the 

 most characteristic features of this class of Worms. The 

 proboscis is hollow : when it is extended to its utmost, a 

 part still remains which is not capable of being everted, and 

 at the junction between the eversible and non-eversible 

 parts, i.e., at the extremity of the organ when it is fully 

 protruded, there is in many of the Nemerteans a pointed or 

 serrated stylet (Fig. 74, st.), which probably permits of the 

 proboscis being used as a weapon : when a stylet is absent, 

 the surface of the extremity is sometimes abundantly 

 provided with stinging-capsules; sometimes it is beset with 

 glandular adhesive papilla. The proboscis is capable of 

 being retracted within the interior of an investing sheath, the 

 proboscis sheath. 



The alimentary canal (Fig. 73) is a simple tube, distin- 

 Man. Zool. L 



