1^1, Pomona College Journal of Entomology and Zoology, Vol. IX, No. 2, June 



The Nervous System of AracodaSemima- 



culata and the Description of a Method 



of Stereographie Reconstruction 



WILLIAM L. HAMILTON 



Aracoda semimaculata, oi the family Lumbriconereidae (poly- 

 chaetous 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 ot 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 taet that it is laid on in exceedingly 

 thin lamina' it presents a beautifully iridescent surface. 



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

 pressed organ which is practically made up ot 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. .>). Hie body segments are unianu- 

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

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

 being distinctly longer than the notopodium and bent up finger- 

 like at the tip. 1 he notopodium appears as a broadly rounded dis- 

 continuation ot the upper hall ol the body ot the parapodium. It 

 is equipped with a varying number ol winged pointed seta' and 

 blunt uncinate seta'. The front and hind parapodia become less 

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



Mi.n ions 



Fixation. A large number ot the worms, fixed in aeetie sub- 

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

 mer at the Laguna Marine I aboratory, transferred to Si) per cent 

 alcohol and saved tor study the following winter in Claremont. 

 1 hose fixed m the aeetie mixture could easlv be sectioned whole in 



