44 



Arenicolidae 



absence of a lamina along the distal portion, and in the 

 nature and comparative abundance of the processes present 

 in that region of the chaeta. 



The most highly developed notopodial chaetae present in 

 the genus are found in A. loveni. In the notopodia of this 

 (and some other) species the chaetae seem to be in two more 

 or less distinct series, an anterior and a posterior ; the 

 chaetae of the anterior are shorter than those of the posterior 

 row, but they have the same form and structural detail. 

 The longer chaetae are about 6*6 to 6 • 8 mm. long, and the 

 shorter ones 5'3 to 5*6 mm. Each has a moderately 

 uniform diameter for the greater part of its length, but in 

 its distal portion tapers to a fine point. For a distance of 

 1 to 1*3 mm. behind the tip, there is, along one edge of 

 the chaeta, a well-marked lamina (Fig. 11 a), which attains 

 a breadth of 15 yu. and, as seen under medium magnification, 

 is marked by closely set oblique lines and has a finely 

 dentate margin. The opposite edge of the chaeta bears 

 numerous regularly arranged processes, which, under low 

 or medium magnification, appear as fine teeth projecting 

 at an angle of about 30° to 40° from the shaft of the chaeta, 

 but which, examined with an immersion lens, are seen to 

 be crests passing round the shaft (Fig. 11 b). The undivided 



base of each crest is fixed to 

 the shaft, and the distal por- 

 tion of the crest, that is, its 

 free margin, is subdivided 

 into a large number of fine 

 teeth. Each crest appears 

 to be a comb-like structure, 

 bent so as to envelop the 

 greater part of the shaft of 

 the chaeta, the curved por- 

 tion of the crest being seen 

 in profile where it projects 

 from the shaft. The regu- 

 larly ari'anged structures 

 visible, under low power, as 

 fine teeth along one margin 

 of the chaeta are, then, the 

 crests seen in profile, and 



'ig. 11. — A. loveni. A, Distal third of a notopodial 

 chaeta, fi'om a specimen 335 mm. long ; IJ, The region 

 marked + in A more highly magnified. 



