ANATOMY AND CLASSIFICATION OF THE ARENICOLIDiE. 447 



it is accompanied by one^ two, or three capillary setse. In 

 the segments anterior to them the crotchets are confined to 

 the neuropodia, the notopodia bearing only the capillary 

 setge described above (p. 445). Mesnil (1897) found a similar 

 condition in the last six to twelve segments of his specimens 

 of Clymenidesecaudatus (= Arenicola ecaudata), and 

 in the last six segments of his C. incertus. In his account 

 of the development of A. cristata, Wilson (1882) figures 

 a larva eight days old, which bears five paired groups of 

 setee, each of which groups contains a single crotchet aloug 

 with one to four capillary setse. The crotchet is figured, 

 however, distinctly ventral to the capillary sette, and may 

 belong to the neuropodium, aa Wilson thought, though the 

 first three (and sometimes four) segments of the adult to 

 which these segments of the larva correspond are devoid 

 of neuropodia. As the single crotchet is present only in 

 the last formed, i. e. youngest notopodia of A. ecaudata, 

 and in recently formed segments of A. cristata, it there- 

 fore appears probable that for some time after its forma- 

 tion each notopodium bears a crotchet, but very soon the 

 crotchet is lost, and henceforward the notopodium bears capil- 

 lary setae only. It is interesting to note in Wilson's figures 

 of the post-larvffi of A. cristata (1882, PL XXI, figs. 60, 61) 

 that each notopodium bears one laminated seta similar to 

 those of the post-larval A. marina described above (p. 445), 

 accompanied by one, two, or three ordinary capillary setee. 

 There are other examples of parapodia of polychgetes bearing 

 both crotchets and capillary sette, e. g. the Capitellidte. In 

 Notomastus (Eisig, 1887, p. 565) the segments of the 

 thorax bear laminated capillary setge similar to those described 

 above in the notopodia of the post-larval Arenicola marina 

 (p. 445), while the parapodia of the first eighty segments of 

 the abdomen bear both laminated capilliform setee and 

 crotchets. In Capitella (Eisig, 1887, pp. 565, 566), also, 

 laminated setse and crotchets occur together in the same 

 parapodium of one segment of the thorax. Thus, in young 

 specimens 1 mm. to 3 mm. long, they are present together in 



