312 PROCEEDINGS OF THE ACADEMY OF [April, 



The first two or three are smaller and of simpler structure than the 

 others, consisting of small contiguous notopodial and neuropodial 

 setigerous areas and behind each a postsetal lobe of which the notopodial 

 is narrow, erect and pointed triangular, the neuropodial a low, broad, 

 feebly pectinated fold, corresponding to the larger size of the latter. 

 The neuropodium increases in size rapidly and soon becomes a low plat- 

 form rising toward the caudal margin and bearing the setse in a close 

 phalanx of several, gradually rising tiers. They attain the maximum 

 size at IX to XIII on which the setae palisade is about four times as 

 deep as long, and the now conspicuous postsetal fold bears twelve to 

 fourteen or fifteen marginal processes (PL XXI, fig. 172), of which the 

 dorsal is frequently somewhat larger than the others and occupies a 

 more detached position above the setse. (3n somites XII to XV, 

 inclusive, the ordinary palisade setse are much reduced and in part 

 replaced in the dorsal portion of the posterior row by a few stout 

 spines, the dorsalmost of which is very large and provided with a 

 special cirrus, at the l^ase of which opens a large pyriform gland, 

 sometimes visible to the naked eye as a whitish swelling on the surface 

 of the postsetal fold (PI. XXI, fig. 174). At the same time the entire 

 neuropodium undergoes reduction from the ventral side and the 

 postsetal fold becomes smaller with few marginal processes. Except 

 that it gi-adually shifts dorsad and becomes larger, with a conspicuous 

 asymmetrical wing on the ventral side of the base, the notopodial 

 postsetal lobe undergoes no change in the anterior region. At somite 

 XVI the neuropodium becomes abruptly reduced in size, turned dorsad 

 as a narrow erect process, which may bear one or two small papillsp 

 on its lateral margin but often lacks them, and is elevated upon a 

 winglike compressed base which unites it to and also bears the noto- 

 podium. Just above its base the neuropodium is constricted, and 

 distally is divided into a short, truncate, postsetal lip and a longer 

 postsetal and ventral acute conical lip (PI. XXI, fig. 173) between 

 which the acicula end and the small tuft of setae arises. The noto- 

 podium of XVI consists of a setigerous tubercle bearing a large spread- 

 ing fascicle of setae and provided with an erect, broad, lamellar, asym- 

 metrical ovate, postsetal lip which is abruptly constricted at the end 

 to a slender attenuated tip reaching nearly to the tips of the setae. 

 On succeeding segments parapodia (PI. XXI, fig. 173) continue to 

 change in the direction initiated on XVI, the thin basal plate rising- 

 higher and the notopodia and neuropodia becoming more slender 

 and erect until they become strictly dorsal, with the two small erect 

 rami elevated on a lamelliform pedicle. The lips of the neuropodium 



