216 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



tions : — (1) an anterior bearing parapodia, but no gills, 



(2) a middle region bearing both parapodia and gills, and 



(3) a posterior portion or tail, which has neither setae nor 

 gills. Each of these parts is composed of a number of 

 segments, but the segmentation is somewhat obscured by 

 the sub-division of each segment into a number (generally 

 five) of rings or annuli. 



One of the annuli of each segment is larger than the 

 rest and bears the parapodia. The latter may be best 

 seen in the middle branchiferous segments. They are 

 obviously much reduced compared with those of Nereis, 

 and their two rami are different in shape and more dis- 

 sociated than they are in Nereis. The notopodium is a 

 small conical elevation situated dorso-laterally, on the 

 rounded apex of which is the mouth of the setal sac from 

 which the tips of a small pencil of hair-like setae project 

 to a greater or lesser extent (fig. 19). The neuropodium 

 is a muscular ridge traversed dorso-ventrally by a narrow 

 slit, the mouth of the setal sac, in which are situated in 

 a linear series the numerous chaetae or crotchets. The 

 first few neuropodia are small, but in the posterior part of 

 the branchial region they are well developed and extend 

 ventrally until those of the right and left sides almost 

 meet in the mid-ventral line. Each has the appearance 

 of a pair of closely applied tumid lips between which only 

 the tips of the curved chaetae project. There are no cirri 

 or acicula in the parapodia of Arenieola. For a detailed 

 description of the setae, see p. 223. 



There are thirteen branchiferous segments, and in 

 the region in front of the first gill six chaetigerous 

 segments may be recognised. The interval between two 

 chaetigerous annuli is sub-divided into four rings, except 

 between the first and second chaetigerous annuli, where 

 there are only two rings, and between the second and 



