178 



UNSEGMENTED " IVOJiMS." 



open to the exterior is rhythmically contractile. It has also 

 been suggested that they are sensory. 



Se/ise Organs. 

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

 associated with the superficial nerve plexus already men- 

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

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

 cases otocyst sacs have been observed. 



Alimeniary System. 

 A ventral mouth leads into a plaited oesophagus, which is 

 followed by an intestine with regularly arranged lateral Cfeca. 



Fig. 58. — Transverse section of a Nemertean — Carinclla. 

 (After BiJRGER.) 



i/.«., Dorsal ner\'e ; fi.c, proboscis cavity ; g.^ gut ; C-w., circular 

 muscles ; l.m., longitudinal muscles ; d.v.in.^ dorso-ventral muscles ; 

 Lv., lateral vessel. 



Between the CEeca run transverse muscle partitions. The anus 

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

 the cseca 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- 



