47 



X IJOO 



Fig. 15.-^4. pu«Ula. The 

 end of a fractured 

 chaeta, from a large 

 speciiuen from T'n- 

 alaska. 



Chaetae of Arenicola 



cliaetae, may attain a width of 15 to 20 /a. 

 The himina may be entire at its margin, and 

 crossed by numerous tine 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 Siigeblatter, 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. afisimilis. 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. 



2^7(silla also present con- 

 siderable differences in the 



degree of their " hairi- 

 ness," some closely resem- 

 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. ijusilla, is represented in Fig. 15, and 

 shows the Sagebliitter ; the figure would serve 

 almost equally well for a chaeta of A. marina. 

 The chaetae of A. ccandata and branchi- 

 alis are identical in form and characters. 

 Although they are as stout basally as chaetae 

 of the same lengtli 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 ^, ^-pmiiihiaiis. xipofauoto- 



•' nniiifil r'napta. surface \new 



Fig. 16. — A, A. ecaudata. Distal 

 half of a notopodial chaeta, 

 seen in optical section. 



podial chaeta, surface \iew. 



