ASHWORTH, AN ACCOUNT OF ARENTCOLA LOVENI KINBERG. 9 



setae of the anterior rovv are rather shorter than those of the 

 posterior row but they have the same form and structural 

 detail. The setae of the ninth notopodia of one of the Sal- 

 dan ha examples were examined in detail. The longer ones are 

 about 6,6 to 6,8 mm. in length, the shorter ones 5,3 to 5,6 

 mm. For a distance of l,o to I.3 mm. behind the tip each 

 seta bears, along one edge, a well marked lamina which at- 

 tains a breadth of of 15 [j., and, as seen under medium magni- 

 fication, is marked by closely set oblique lines and has a 

 finely dentate margm (Fig. 3). The other margin of the seta, 

 for a distance of 1,5 to 1,7 mm. from the tip, bears numerous 

 regularly arranged structures which, seen imder low or me- 

 dium magnification, look like long fine teeth; similar struc- 

 tures are also present along the laminate side of the seta 

 for a short distance proximal to the lamina. In most spe- 

 cies of Arenicola the »teeth», corresponding to those just 

 described, are more closely pressed to the shaft of the seta, 

 whereas in A. loveni they project at an angle of 30° to 40° 

 from the shaft and are consequently much more obvious, 

 especially as in A. loveni they are also of larger size. The 

 exact nature of these outgrowths on the shaft of the seta 

 is difficult to determine but, under an immersion objective, 

 it is seen that they are regularly arranged crests passing 

 round the shaft (Fig. 4). The apparently undivided base of 

 the crest is fixed to the shaft and its distal margin, that is, 

 its free edge, 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 portion of the shaft of the seta, the 

 curved portion being seen in profile where it projects beyond 

 the edge of the shaft. The regularly arranged structures, 

 seen under low power, as fine teeth along one margin of the 

 seta are, then, the profile views of these crests, which remind 

 one of the similar crests or »Sägeblätter» present on the setae 

 of some Aphroditidae and certain other Polychaeta. The 

 laminate portion of the seta bears on its surface numerous 

 fine processes the pointed tips of which are directed at slightly 

 different angles; those seen in profile at the margin of the 

 lamina form a regular series of very fine teeth. In each in- 

 terval between the »Sägeblätter>> there is a denser transverse 

 band, the presence of which, at regular intervals of about 

 10 — 12 [x, gives to the distal portion of the shaft of the seta 



