52 bulletin: museum of comparative zoology. 



The presence of remarkably large and numerous cephalic nerves 

 m Carustella (Text-tig. 2) and Carinomella (PI. 6, tig. 53), 

 although ocelli are wanting, indicates the presence of abundant 

 cephalic sense organs. 



In many hoplonemerteans three to live pairs of large and pro- 

 fusely branching cephalic nerves supphdng the ocelli and other 

 organs of the head can often be distinguished in life. These arise 

 from the anterior border of the dorsal ganglia. 



Esophageal nerves. — In all nemerteans in which the mouth is 

 situated behind the brain (Paleo- and Heteronemertea), a pair of 

 nerves originate from the ventral ganglia and suiijily the mouth 

 region and anterior portions of the esophagus (PI. 15, tig. 90). 

 After their origin these nerves are commonly connected with each 

 other by one or more (sometimes numerous) commissures, and often 

 have secondary unions with the ventral ganglia. They end in tine 

 branches a short distance behind the mouth, and supply the epithe- 

 lium of the buccal cavity and anterior end of esophagus. 



Proboscidial nerves. — The proboscis in all Paleo- and Hetero- 

 nemertea is provided Avith a single pair of large nerves which are 

 situated on the right and left sides of the organ and extend through- 

 out its whole length. They usually arise fi'om the ventral commis- 

 sure near the ganglia, and enter the proboscis at its insertion among 

 the tissues of the head in the region of the brain commissures. 



In the Paleonemertea they take up a position immediately between 

 the inner epithelial lining and the musculatiu'e (PI. 12, tig. 80 ; PL 

 11, tigs. 66-70 ; PI. 15, tig. 90). Here they send out branches to 

 form a more or less conspicuous plexus, but do not branch out so 

 much as to lose their identity. 



In those Heteronemertea in which only two muscular layers are 

 developed in the proboscis (most Taeniosomidae and certain Lin- 

 eidae) the nerves take a position, as in the Paleonemertea, beneath 

 the inner epithelinm, but in all those forms in which the prol)Oscis is 

 provided with three muscular layers the nerves lie between the inner 

 longitudinal and the circular nuiscles. In all these forms the nerves 

 send out very numerous branches which spread out into a conspicu- 

 ous nervous plexus. In some species, moreover, this distribution of 

 the nerve fibers into the plexus is so complete that the nerve cords 

 can no longer be recognized. This is particularly the case in the 

 Taeniosomidae. 



