Chaetae of Arenicola 



chaetae, may attain a width of 15 to 20 /it. 

 The lamina may be entire at its margin, and 

 crossed by numerous fine oblique lines, or it 

 may be breaking up, from the edge inwards, 

 along the course of the oblique striae, so 

 that its margin becomes denticulate. On 

 the opposite side of the chaeta and pressed 

 closely to the shaft, are Sageblatter, the spines 

 of which are smaller than in A. cristata. 

 Figs. 13 A, B (the latter 

 an optical section) are 

 drawn from the chaetae 

 of A. marina, but the 

 figures would serve also 

 for some specimens of 

 A. assimilis. The chaetae 

 of the latter species are, 

 however, usually rather 

 less hairy and the spines 

 are smaller (Fig. 14) than 

 those of A. marina, but 

 examples from different 

 localities have been found 

 to exhibit variation in this 

 respect. Chaetae of A. 

 pusilla also present con- 

 siderable differences in the 

 degree of their "hairi- 

 ness," some closely resem- 

 U K- ble those of A. marina, 

 than which, however, they 

 are usually rather less hairy. The fractured 

 end of a large chaeta, from a massive example 

 of A. pusilla, is represented in Fig. 15, and 

 shows the Sageblatter ; the figure would serve 

 almost equally well for a chaeta of A. marina. 

 The chaetae of A. ecaudata and branchi- 

 alis are identical in form and characters. 

 Although they are as stout basally as chaetae 

 of the same length from the caudate species, 

 they begin to taper nearer to the proximal 

 end, and their distal portion is consequently 

 more slender. The newly formed chaetae of B > A 



47 



chaeta f from 

 specimen from 



alaska. 



16 _ A ^ ecaudata Digtal 



chaeta> 

 Tip of a noto- 



podial chaeta, surface view. 



