126 A renicolidae 



Arenicola marina, partim 



Marenzeller, Zool. Jahrb. Abt. Syst., iii (1888), p. 12 

 Ives, Proc. Acad. Nat. Sci. Philad. 1890 (1891), p. 74. 



Arenicola piscatorum Cuv. [sic] var. 



Grube, Monatsb. K. Preuss. Akad. Wiss. Berlin 1877 (1878), p, 511 

 (Kerguelen). 



The variety affinis has nineteen segments ; thirteen pairs of gills, 

 the first, which is on the seventh segment, may be small or absent. 

 Other characters as given above (p. 124). 



HISTORICAL ACCOUNT. The species A. assimilis was founded by 

 Prof. Ehlers on examples collected by Dr. Michaelsen in the Strait 

 of Magellan. Prof. Ehlers stated that these worms appeared to be 

 so closely similar to A, marina that, at first sight, he took them for 

 examples of this species, but the presence of the first gill on the 

 eighth segment, together with the provenance of the specimens, 

 seemed to him to justify their separation from A. marina, as a, 

 closely allied species. He also remarked that the middle prostomial 

 lobe seemed to be proportionately smaller in these specimens than in 

 A. marina, and the dorsal chaetae more feebly "feathered." In 1901 

 Prof. Ehlers stated that the gut, vascular system and nephridia of 

 A. assimilis agreed, as far as he had been able to ascertain, with 

 those of A. marina, but there were differences in regard to the 

 statocysts, and the position of the external apertures of these organs, 

 which were apparently nearer the brain in A. assimilis. 



The writer (1903) gave a full account, with figures, of the 

 anatomy of A. assimilis, based on the study of co- types from 

 Uschuaia and Punta Arenas, and showed that this species has 

 twenty * chaetiferous segments, that the prostoinium differs in form 

 from that of A. marina, that the oesophageal glands are multiple, 

 septal pouches are absent, the ventral lips of the nephridia are 

 peculiarly frilled, and that the statocysts are remarkable for their 

 large size. He also described examples from Otago Harbour, New 

 Zealand, and Macquarie Island, belonging to the species assimilis, 

 but differing from the type in having nineteen chaetiferous segments, 

 and statoliths of purely external origin 2 quartz grains, etc. The 



1 This unusual number of segments was not the subject of comment by 

 Prof. Ehlers ; he seems to have been more impressed with the unwonted 

 position of the first gill. 



12 Those of the Fuegian specimens were spherical, and composed almost 

 entirely of secreted substance. 



