244 ARCHI ANNELIDA 



Protodrilus and Polygordius are distinctly Annelidan in 

 character. Protodrilus 1 is found in the mud of the " Pantano," 

 an inlet of the sea near Messina ; whilst of Polygordius 2 one 

 species at least occurs on our shores, and several ,others in the 

 Mediterranean and elsewhere. The worms are cylindrical, with 

 many segments, but these segments are only indistinctly marked 

 externally by girdles of cilia in Protodrilus, or by faint grooves 

 in Polygordius; but there are none of the characteristic Chaetopod 

 bristles or chaetae. The small prostomium which overhangs 

 the mouth is provided with a pair of ciliated pits, and carries a 

 pair of tentacles, serving as sensory organs, which, in Protodrilus, 

 are also respiratory. The anus is surrounded by glandular 

 papillae in Polygordius, by means of which the animal can fix 

 itself; these are represented in Protodrilus by a couple of processes. 



The nervous system lies entirely in the epidermis. The body- 

 cavity is regularly segmented by transverse septa passing from the 

 body- wall to the intestinal wall. The foregut presents a slight 

 eversible portion in Polygordius, whilst in Protodrilus it has 

 a peculiar U-shaped muscular diverticulum on its ventral surface, 

 corresponding with the similar apparatus in Dinophilus ; it is 

 capable of eversion, and aids the worm in burrowing, as well as 

 in seizing and swallowing the mud. The vascular system is re- 

 presented by a dorsal and a ventral vessel, neither of which, how- 

 ever, is contractile. In Protodrilus the dorsal vessel divides into 

 two branches in the first segment, each of which passes to the tip 

 of the tentacle, and returning, joins its fellow to form the ven- 

 tral vessel. In some species of Polygordius there is a pair of 

 vessels connecting the dorsal and ventral vessels in every segment, 

 but no vessel to the tentacle. The blood is colourless in some 

 species of Polygordius, but may be yellow (P. neapolitarius), red 

 (P. lacteus), or green (P. erythrophthalmus). Paired nephridia, 

 with distinct funnels, occur regularly throughout the body. 



The sexes are separate in Polygordius, whilst Protodrilus is 

 hermaphrodite, bearing ova in the first seven segments and 

 testes in the remaining segments. The genital cells are produced 

 from the body- wall in every segment ; their mode of discharge is 

 unknown in the male Polygordius, though probably the nephridia 



1 Hatschek, Arb. Zool. Inst. Wien, iii. 1881, p. 79. 



2 Fraipont, "Le Genre Polygordius," Fauna u. Flora des Golfes v. Ncapel, 

 Monogr. xiv. 1887. 



