CHAETOPODA: ARCHI-ANNELIDA. 613 



nereis, cf. also Ehlers, Borstenwiirmer, 1868, p. 451, &c.; and Bobretzky, A. N. 37 

 (2), 1871, p. 385. 



Powers of reparation : in Diopatra, Ehlers, Akad. programme, Erlangen, 1869 ; 

 cf. A. N. 35 (2), p. 244; in Spio, Bobretzky, A. N. 37 (2), 1871, p. 385; cf. de 

 Quatrefages, Hist. Nat. (supra], p. 124; in Oligochaeta, p. 208-9 ante - Phos- 

 phorescence, p. 201, and p. 208 with note i. 



Freshwater Polychaeta of Trinidad, von Kennel, Arb. Zool. Zoot. Inst. Wurz- 

 burg, vi. 1883. Manayunkia, Leidy (supra). Boring Chaetopoda, Ray Lankester, 

 A. N. H. (4), i. 1860; Mclntosh, ibid. ii. Pelagic forms , Viguier, C. R. 101, 1885 ; 

 Greeff, Z. W. Z. xxxii. 1879. 



ARCHI-ANNELIDA. 



The name Archi- Annelida was employed originally by Hatschek as 

 an ordinal name for the Polygordiidae, a family with a single genus, 

 Polygordius, to which he added subsequently the genus Protodrilus. 

 Foettinger has more recently still added a second family, Histriodrilidae, 

 represented by the parasitic Histriodrilus Benedeni (= Histriobdella 

 Hoinari). All the Archi-annelids are marine ; all have a small pro- and 

 a large peri-stomium ; the somites of the body are similar to one another, 

 especially in the Polygordiidae, and are but feebly marked externally. 

 There are no setae, no parapodia, cirri or branchiae, but the head carries 

 two or more tentacles. The muscles form a single layer of longitudinal 

 fibres disposed in four bands, two dorso-lateral, two ventro-lateral, the 

 latter widely separate. Polygordius Villoti is stated by Perrier to have 

 circularly disposed fibres. The nervous system is retained in the hypo- 

 dermis. A pair of ciliated grooves is present on the head. The 

 oesophagus is restricted to the peristomial somite, and there is a simple 

 intestine. A muscular sub-oesophageal bulb or proboscis lies beneath the 

 oesophagus and at the posterior margin of the mouth in Histriodrilus 

 and Protodrilus. Simple nephridia are present. Histriodrilus and Poly- 

 gordius are of separate sexes ; Protodrilus is hermaphrodite. 



The Histriodrilidae are the higher group, inasmuch as there are 

 individual nerve ganglia and special (?) genital ducts. The Polygordiidae 

 have an intra-muscular nerve-plexus connected to the cells of the hypo- 

 dermis, and oblique dorso-ventral muscles are present in each somite, as 

 in many Polychaeta. Polygordius, like some Nemertea, is apt to break 

 into fragments when irritated or injured. 



Histriodrilus Benedeni ( = Histriobdella Homart) is parasitic upon 

 the Lobster, the eggs of which it devours. It is a minute worm 1*4 mm. 

 long. There is a distinct head, a body composed of three narrow somites, 

 a sexual enlargement which appears to include two (? 3) somites followed 

 by three short somites. The head carries a median and two laterally 

 placed pairs of sensory tubercles, and a pair of short limbs. The last somite 



