COE : NEMERTEANS OF WEST AND NOETHWEST COASTS. 



53 



In the Hoplonemei'tea the number of proboscis nerves varies 

 greatly in different species of the same genus, but is fairly constant 

 for all individuals of the same species. Thus Amphiporus similis 

 and A. tnacraccoithns have each 10 proboscis nerves ; A. flavescens 

 and A. calif ornicKS 10, 11 or 12; A. punctatulus 12 or 13; A. 

 bimaculatus 14 or 16; A. nebulosus IT; and A. angidatiis 17 to 20, 



Fig. 19. — Amph iporvs angulatiis. Transverse section through ventral commissure 

 of brain, showing dorsal attachment of proboscis to tissues of head. Anterior 

 ends of nephridial tubules {nep) appear in right half of section ; smg, sub- 

 muscnlar glands ; p/i, proboscidial nerves. 



but usually IS. Nearly all species of Tetrastemma have 10 pro- 

 boscidial nerves, while some forms of Drepanophorus have more 

 than 30. 



In many hoplonemerteans all the proboscis nerves originate 

 directly fi'om the anterior border of the brain, although in A. 

 angulatus (Text-fig. 1 9) and some other forms those arising fi'om each 

 side of the brain are at lirst more or less fused into a single trunk 

 which breaks up into a definite number of independent nerves after 

 reaching the proboscis. 



In all hoplonemerteans the nerves lie imbedded in the midst of 

 the longitudinal muscular layer in the portion of the proboscis 



