1 78 UNSEGMENTED "WORMS." 



open to the exterior is rhythmically contractile. It has also 

 been suggested that they are sensory. 



Sense Organs. 



Nemertines are very sensitive, and in many this is to be 

 associated with the superficial nerve plexus already men- 

 tioned. Tactile papillae and hairs are also present in some. 

 Eyes and eye spots are of general occurrence, and in some 

 cases otocyst sacs have been observed. 



Alimentary System. 



A ventral mouth leads into a plaited oesophagus, which is 

 followed by an intestine with regularly arranged lateral caeca. 



d.n 



FIG. 58. Transverse section of a Nemertean Carinella. 

 (After BURGER.) 



d.n., Dorsal nerve ; fl.c., proboscis cavity ; g., gut ; c.vt., circular 

 muscles ; /.;;/., longitudinal muscles ; d,v.m., dorso-ventral muscles ; 

 /.?/., lateral vessel. 



Between the caeca run transverse muscle partitions. The anus 

 is terminal. In the adults of the primitive genus, Carinella, 

 the caeca are absent, but they are present in the larva. 



The Proboscis. 



In a cavity along the dorsal median line there lies a 

 remarkable organ, known as the proboscis. It is protruded 

 and retracted through an opening above, or, in a few cases, 

 within the mouth, but it has no connection with the ali- 



