216 M. E. ClaparMe on a new Genus 



All these genera consist at present only of freshwater spe- 

 cies. It is therefore interesting to make full acquaintance 

 with a marine form, which certainly differs much from the 

 types hitherto described, so that I have been obliged to form 

 for it a new genus, which I will characterize further on under 

 the name of Hemidasys *. 



Hemidasys agaso lives abundantly in the most muddy 

 parts of the port of Naples ; hence its specific name [agaso j 

 groom). For a long time I regarded it as an epizoon. The 

 surest means of procuring it is to examine carefully the speci- 

 mens oi Nereilepas caudata (Spio caudatuSj DelleChiaje). We 

 soon meet with some individuals bearing one or two specimens 

 of Hemidasys : these are fixed by their posterior extremity be- 

 tween the feet of the Annelide. Their body, which is very 

 contractile, elongates and contracts alternately, the anterior 

 extremity feeling rapidly about in all directions, to seek its 

 nourishment among the setae of the Nereilepas. Their move- 

 ments resemble those of many of the Rotatoria. In attentively 

 examining the mud, we find several free Hemtdasyes, their 

 being parasites, therefore, is only occasional or accidental. I 

 have, however, never met with Hemidasys on other Annelides 

 in the mud except Nereilepas. 



Hemidasys ayaso attains a length of 0*3 to 0*5 millim., with 

 an average breadth of 0'12 millim. Its form is that of a 

 small band, or thick strap, with nearly parallel margins. In 

 general it is more flattened than most of the other Grastro- 

 tricha. The surface of the body is formed by a delicate 

 cuticle separated from the adjacent parenchyma by a stratum 

 of liquid of a slight rose-colour. The colour of this liquid is 

 probably due to a simple effect of contrast, like that of the 

 vacuoles and the contractile vesicles in the Infusoria. The 

 liquid stratum is traversed by a great number of little bands, 

 which pass directly from the parenchyma to the cuticle. At 

 the point where it is attached to the latter, each band dilates a 



result. ('Zur Kenntniss kleinster Lebensformen nach Bau, Function, 

 Systematik, &c., von Dr. Maximilien Perty,' Bern, 1852, p. 35.) 



* M. Mecznikow also mentions the genus Sacculus, Gosse. On the 

 other hand, the Russian naturalist does not mention Dasi/dites, Gosse, 

 the diagnosis of which nevertheless dates back to 1851 (Ann. & Ma^. 

 Nat. Hist. Sept. 1851). In any case the genus Saccidtis has nothing to do 

 here. It was, it is true, classed originally among the Holotricha, Ehrb. ; 

 but this not very natural order contains, besides some Gastrotricha, cer- 

 tain true Rotatoria. The Sacculi have a mastax with two hammers and 

 an incus. Their males are destitute of digestive apparatus ; in short, they 

 are true Rotatoria in all points. M. Mecznikow certainly did not know 

 them when he enumerated them among the Gastrotricha. Mr. Gosse, 

 moreover, in his recent work on this group makes no mention of tliom. 



