The Nervous System of Aracoda Semima- 



culata and the Description of a Method 



of Stereographic Reconstruction 



WILLIAM F. HAMILTON 



Aracoda semimaculata, of the family Lumbriconereida; (poly- 

 chstous annelids) is found in great abundance in the mussel beds 

 near Laguna Marine Laboratory. In length the worm may be 

 from five to fifty cm. and in diameter, from two to six mm. In 

 general appearance these worms resemble the earth worm, being 

 without palpi, or tentacles and usually of a reddish brown color. 

 Pigmentation, however, varies from a deep reddish brown to a pale 

 yellow. The cuticle is a tough chitinous membrane clear yellow in 

 cross section, but due to the fact that it is laid on in exceedingly 

 thin laminee it presents a beautifully iridescent surface. 



The prostomium (Fig. 1), is a blunt, ovoid and slightly de- 

 pressed organ which is practically made up of nervous and sensory 

 tissue, constructed and inter-related in a very complex manner. The 

 peristomium is about as long as the prostomium and twice as long 

 as the body segments (Fig. 3). The body segments are unianu- 

 late and very distinct. The parapodia ( Fig. 3 ; a ) , are biramous, the 

 neuropodium, typically — in the middle segments of the worm — 

 being distinctly longer than the notopodium and bent up finger- 

 like at the tip. The notopodium appears as a broadly rounded dis- 

 continuation of the upper half of the body of the parapodium. It 

 is equipped with a varying number of winged pointed seta? and 

 blunt uncinate set^. The front and hind parapodia become less 

 and less typical as the ends of the worm are approached. 



METHODS 



Fixation. A large number of the worms, fixed in acetic sub- 

 limate and in hot mercuric chlorid were prepared during the sum- 

 mer at the Laguna Marine Laboratory, transferred to 80 per cent 

 alcohol and saved for study the following winter in Claremont. 

 Those fixed in the acetic mixture could easly be sectioned whole in 



