8- Journal of Comparative Neurology. 



two pairs, set very close together, of long slender appendages— the 

 cephalic cirri. One cirrus of each pair is over twice as long as the 

 other one. Each cirrus is inserted on a short basal part similar to but 

 smaller than the basal part of a palp, and is kept constantly moving in 

 all directions. The surface of the peristome and of a few of the an- 

 terior metameres is marked by numerous grooves which pass obliquely 

 from their anterior to their posterior borders. Each metamere back of 

 the peristome bears on each lateral surface a parapodium — a lobed out- 

 growth of the body wall {see Text-figure 2). A typical parapodium 

 consists of about seven comparatively flat, pointed lobes which func- 



Text-figttre 2. Outline of a typical parapodium of Nereis virens. d. dr., 

 dorsal cirrus; g., gill lobe; v. dr., ventral cirrus. 



tion as gills and of two slender pointed appendages - the dorsal and 

 ventral parapodial cirri — which are purely tactile. The anterior para- 

 podia are very small ; passing caudally they increase in size until near 

 the caudal end of the worm. At this extremity, the metameres be- 

 come very small ; the parapodia also decrease in size but are much 

 larger in comparison with the size of the metameres than are the para- 

 podia of the cephalic end of the worm. The anal metamere bears a 

 pair of long slender appendages similar to the cephalic cirri and known 

 as the anal cirri. These cirri are directed backwards. 



IV. The Diffuse Sense Organs. 



The diffuse sense-organs are found not only in the epider- 

 mis over the entire body but also in each of the cephalic and 

 anal appendages and in each lobe of every parapodium. Each 

 organ consists of a small elongated group of bipolar nerve-cells 

 whose central ends taper into nerve fibers which pass into the 

 central nervous system, and whose peripheral ends also taper 

 into processes which pass through modified areas in the cuticula 



