Arenicola branchialis 145 



SIZE. Average British or French specimens of A. branchialis are 

 about 150 mm. long, when extended normally; the longest seen by 

 the writer reached a length of 250 mm. Specimens from Naples and 

 the Black Sea have a thinner body wall and are less robust than the 

 preceding, and seldom exceed 100 mm. in length. 



COLOUR. Examples of Arenicola branchialis from the Atlantic 

 shores of Great Britain, France, Spain and Northern Africa, range in 

 colour from bluish black to dark green, brown, and light reddish 

 brown, but the majority are very dark. The specimen represented 

 in PI. II, Fig. 5, exhibits the typical colouration of British specimens, 

 and indicates the greenish iridescence so frequently associated 

 with the anterior region. A few examples from the localities above 

 named exhibit lighter colours, similar to those shown in the figure 

 of A. ecandata on PI. II, Fig. 7. 



Neapolitan specimens are generally dark iridescent green in 

 their anterior and posterior regions, and dark reddish brown in the 

 middle region of the body, but occasionally a lighter specimen 

 yellowish red in colour is met with. 



VARIATIONS IN THE ORGANS. The number of segments is subject 

 to much variation ; most specimens have lost some of their posterior 

 segments and thus exhibit fewer than they possessed at the end of 

 the post-larval stage, when forty to forty-three were present. The 

 number of segments in this species is therefore about twenty fewer 

 than in A. ecaudaf.a, in which there may be sixty to sixty-four. 

 Average specimens of A. branchialis have about thirty segments. 

 The gills are liable to reduction anteriorly (see p. 142) and posteriorly, 

 the last one to four segments being not uncommonly abranchiate. 



The first notopodium' is either minute or wanting in about 30 per 

 cent, of the specimens examined, but the corresponding neuropodia 

 are well developed (PI. II, Fig. 6). 



PERIOD OF MATURITY, DEVELOPMENT. In the Irish Sea and the 

 English Channel the breeding season is about September to October. 

 Lo Bianco states that this species is mature at Naples in winter; 

 specimens examined there by the writer at the end of March, 

 1900 and 1906, were found to have finished spawning. 



The form in which the eggs are laid, and the larval development 

 are unknown. The only known post-larval examples (described 

 on pp. 81, 82) were collected by Mr. 11. Southern, among the " roots " 

 of Laminaria, in Blacksod Bay, Mayo, in September, 1910. 



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