ARENICOLA BEANCHIALIS. 81 



between the basal and the smaller papillae was less than in the larger examples, but this 

 may have been due to the mode of preparation. In some the large basal papillae show a 

 median pit as in A. ecaudata, but the influence of the mode of preparation on this condition 

 has yet to be determined. 



The setigerous processes, as prominent as in A. ecaudata, are somewhat flattened, 

 and the tip has a slight obliquity externally. The bristles have shafts of moderate 

 strength at the base, but finely tapered, as in A. ecaudata, toward the extremity. Fine 

 striae mark the shaft in its more opaque region, and it tapers from a little above the base 

 to the tip. No evident wing is visible, and the sparse whorls of spikes seem to be limited 

 to the slender and transparent tip (Plate GUI, figs. 12 and 12 a). 



There is nothing in the outline of the hook (Plate CIII, figs. 12 b and 12 c) to dis- 

 tinguish it from that of A. ecaudata, for whilst in many of the latter the rostrum is 

 sharper, longer, and bent at a more acute angle, such may only be due to less tear and 

 wear. The striae in both are similar, and a single spine is generally visible in each on the 

 crown of the rostrum. 



The first nephridium is sometimes represented only by a funnel, and each seldom 

 exceeds 7 mm. in length. The vascular ciliated processes of the dorsal lip are less 

 flattened; they are stout, cylindrical and digitiform, generally branched distally. The 

 ventral lip is deeply notched in the centre. There are five pairs of openings, viz. from 

 the fifth to the ninth setigerous rings. 



Habits. — Littoral, under stones in tracks. No regular burrow. It secretes a great 

 amount of mucus, so that in a short time it covers itself in a glass vessel with a gelatinous 

 coating almost of the density of a Salpa. 



This species was discriminated by Audouin and Edwards (1834) at St. Malo by its 

 smaller size and the characteristic number and arrangement of its branchiae. 



Reproduction. — Dr. Ashworth observes that in the Irish Sea and the English Channel 

 the breeding season is from September to October. It is mature at Naples during the 

 winter (Lo Bianco, Fauvel). The gonads appear early on the last four pairs of segmental 

 organs, and in annelids only 35 mm. long. The gonads in the adult are club-shaped or 

 cylindrical. The first has a well-developed gonidial vessel, but no genital cells. The ova 

 are the same size as those of A. ecaudata, viz. 0*136 to 0*14 mm., and have a thick zona 

 (vitelline membrane). 



Claparede (1868) recognised the specific distinctions of Grube's form, to which he 

 gave the name of its author. He corrected the erroneous interpretations of the pro- 

 blematical organs given by Oken, Home, Cuvier, and J. Miiller, and confirmed those of 

 Grube and M. Edwards. Instead of being the generative organs, these are the segmental 

 organs, which Claparede located in segments four to eight. He also figures and describes 

 " auditory organs " — originally mentioned by Mettenheimer. 



Lo Bianco states that the length is 150 mm., while Gamble and Ashworth record it 

 as 225 mm. in the British area. The body resembles that of A. ecaudata ; the arrange- 

 ment of the rings is similar, and the same may be said of the gills. The latter spring 

 from a common origin and show five or six, or more, main stems, which form a kind of 

 rosette, with numerous ultimate branches apparently somewhat dichotomously divided. 

 They diminish posteriorly, the last foot having, perhaps, only a single filament, whilst the 



134 



