. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. Branchionialdane vincenti 149. ! Fig. r)9.—/}. viiiixnli. Anterior end, dorsal aspect; Pk. Prostomium, liearinii groups of eyes ; Per. Peri- stomiuni; Achaetous body- segment, First cliaeti- ferous segment. X 50. laterally groups of eyes (Fig. 59), the number and disposition of wliicli vary a little in different specimens. The peristomium, which is achaetous, is separated from the prosto- luium by a shallow groove. There is no delinite nuchal organ, that is, no pocket- like in
. Catalogue of the Chaetopoda in the British Museum (Natural History). Oligochaeta; Polychaeta. Branchionialdane vincenti 149. ! Fig. r)9.—/}. viiiixnli. Anterior end, dorsal aspect; Pk. Prostomium, liearinii groups of eyes ; Per. Peri- stomiuni; Achaetous body- segment, First cliaeti- ferous segment. X 50. laterally groups of eyes (Fig. 59), the number and disposition of wliicli vary a little in different specimens. The peristomium, which is achaetous, is separated from the prosto- luium by a shallow groove. There is no delinite nuchal organ, that is, no pocket- like invagination of the dorsal epithelium, such as is present in late post-larval and in adult examples of Arenicohi. The next segment, whicli is also witliout chaetae, is homologous with the acliaetous liody seg- ment of Arcnicola (p. 87). Following this are the chaetiferous segments and the bluntly conical pygidium. The number of chaeti- ferous segments depends on tlie stage of growth attained. The largest number observed is fifty-one. Each chaetiferous segment bears notopodial chaetae and neuropodial crotchets. The notopodia and neuropodia of all the preserv^ed specimens are only slightly elevated above the rest of the body wall. The neuropodia are short, being much shorter than those of post-larval ecaudate Arcnicola (cf. PI. XI, Figs. 33, 35). The annulation of the anterior and middle seg- ments is mucli less delinite, and the number of aunuli per segment less constant than in Arenicola. In the larger specimens the segments from the third or fourth to nearly the thirtieth are divided into four to seven ^ rings. The last twelve to twenty segments are generally bi-anniilate, the larger anterior ring bearing the chaetae and the smaller posterior one the gills (PI. XI, Fig. 33). This condition was evi- dently presented also by Langerhaus' specimens (see his Fig. 21 (j), and it seems to be sufficiently constant to be cited as one of the diagnostic features of this worm. Chaetae.—
Size: 1342px × 1862px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondo, bookyear1912
