532 p. W. GAMBLE AND J. H. ASHWORTH. 



We have tested an external character which has not been 

 hitherto much examined — the number of nephridiopores. Of 

 these there are six pairs in A. marina, the last five of which 

 are present in Claparedii, cristata, and Grubii. A. ecau- 

 data is, however, easily separated by the thirteen pairs; the 

 first five of these correspond with those of A. Grubii. 

 Partly, then, because of the close agreement of three fourths 

 of the genus, partly because of the difficulty of detecting the 

 apertures in contracted specimens, the number of nephridio- 

 pores can only be ancillary in systematic work. 



On the whole, then, it must be admitted that the external 

 characters usually relied upon by chtetopodists fail to sepa- 

 rate the species of Arenicola, for though they may be of 

 generic value, the specific differences which they afford are 

 either paralleled by individual variation, or are too slight to 

 admit of satisfactory definition. It therefore behoves us to 

 seek diagnostic characters in the features of the internal 

 anatomy. 



Two years ago we came to the conclusion that Arenicola 

 Grubii and A. ecaudata form a separate section of the 

 genus, characterised by the suppression of the prostomium, 

 the extension of parapodia and gills to the hinder end of the 

 body, and by the possession of closed otocysts, with at first 

 one and afterwards many otoliths, which are secreted from 

 within, not introduced from without. Mesnil has come to the 

 same conclusion, and has suggested a separate genus Areni- 

 colides for these two forms. Such a step appears to us inad- 

 visable. The reduction of the prostomium, and pari passu 

 the simplification of the '' brain," form the most important 

 character which could be adduced to support the erection of 

 a new genus ; for the posterior extension of parapodia and 

 their associated structures, though very valuable for practical 

 purposes of determining forms, is a feature shared by Bran- 

 chiomaldane, and a posterior extension occurs occasionally 

 in A. cristata. The peculiarity of the otocysts is nearly 

 paralleled by A. cristata, which possesses a closed vesicle, 

 but only a single large otolith of endogenous origin. Finally, 



