200 THE ANNELIDA POLYCHAETA. 



the ordinary composite setae in the neuropodium increases. In the somites 

 immediately follomng the seventh the elytra-hke expansions of the notocirri 

 are again lacking, but the notocirri undergo further progressive modifications, 

 coming to appear as a thin membranous wing along the parapodium, with at the 

 distal end a distinct, finger-like process, while the proximal end of the membrane is 

 also free for a short distance ; the acicular process at the end of the notopodium 

 and the other finger-like appendage become longer and about the same in size 

 as the process on the neuropodium. The setae of these notopodia following 

 the seventh are the same as those of the neuropodium, the special coarse setae 

 being abruptly replaced. The neuropodia of the eighth, ninth, and eleventh 

 parapodia remain nearly the same as in the more anterior ones. (Plate 29, fig. 3) . 

 In the twelfth the setigerous process bears at the distal end a thin, mem- 

 branous, leaf-like process which on the thirteenth becomes much larger and 

 narrowly subovate, with the distal end rounded. In the latter, too, the neuro- 

 cirri have become proximally membranous, with a slender, cylindrical, distal 

 process, at one or both sides of the base of which is a low, rounded process often 

 giving the neurocirrus the appearance of being doubled. (Plate 29, fig. 4). In 

 the fourteenth and fifteenth parapodia the membranous appendage to the 

 neuropodium has become still larger and reaches nearly to the ends of the shafts 

 of the setae; it is very finely veined. The notocirral fringe becomes larger, the 

 proximal end free as an angular, distally narrowly rounded lobe, while the distal 

 process is more elongate; it lies conmionly close against the large, non-acicular, 

 notopodial process proximally. At the base of this finger-like, terminal noto- 

 cirral process there are two, slight, rounded lobes on opposite sides. This is 

 the typical form of parapodium prevailing throughout the remaining portion 

 of the body. (Plate 29, fig. 5). In the caudal region the parapodia become 

 reduced in size, but the same structures remain evident and retain the natatory 

 setae throughout. The terminal neuropodial membrane is usually somewhat 

 obliquely subtruncate across the distal end, with a small mucron at the middle. 

 Two acicula in each parapodium, one in each branch. These are black and 

 conspiGuous, finely pointed distad, each extending into a special acicular process. 

 The setae are all compound, but are of three distinct primary types. The noto- 

 podial setae of the first seven pairs of parapodia are of a special type. (Plate 29, 

 fig. 7). They are black or dark brown in color like the acicula. The shaft is 

 gently doubly curved and terminates distally in a deep socket of homogomph 

 form bent a little to one side. The shaft is strongly cross-striate throughout 

 its length. The terminal piece is short and distally blunt or rounded, and a 



