NEREIS DUMERILII. 311 



about the twentieth segment, indicate the transformation. Careful examination of the 

 interior of the feet discloses in these the flabelliform pelagic bristles in process of forma- 

 tion. The spine of the superior division in the abdominal feet shows an enlarged base 

 like a spatula for the attachment of the muscles, which are much longer in the Heteronereid. 

 He points out the increase of the cutaneous glands, especially the verticillate glands of 

 the Heteronereid. The pigment at the moment of transformation undergoes marked 

 changes. In the Heteronereid the cutaneous pigment becomes diffuse and disappears, 

 except in the abdominal region, where brownish transverse lines occur. The peritoneal 

 pigment undergoes resorption, except in the head and the basal segments of the tentacles 

 and palpi. A brown line also occurs in the mid-abdominal region as a new development, 

 for it is absent in the Nereid. The blood-vascular system shows corpuscles (nucleus and 

 coat of protoplasm) in the Nereid, and the dorsal vessel has valves in pairs. These are 

 not seen in the Heteronereid. He also found contractile vascular casca in various 

 regions in this species, e.g., in the feet, and a dichotomous arrangement of vessels. These 

 vessels undergo rapid development during the change of the foot. The muscular fibres 

 become granular and indistinct in the Heteronereid. The proboscis presents remarkable 

 variations in its paragnathi, the epigamous condition having small parallel groups arranged 

 transversely. The maxillae also, he states, show an increase in the posterior or muscular 

 region in the Heteronereid, and generally seven or eight teeth are present. 



Claparede shows a simple, long trumpet-like segmental organ. He says he did not 

 find large examples of N. Dumerilii with sexual elements. They become Heteronereids. 

 The sexual forms range from 15 — 35 mm., rarely the latter. The sexual elements in 

 these develop as in other Nereids, and the ova are 0*41 mm. in diameter. There is no 

 structural difference (externally) between male and female. In March he found a peculiar 

 form in the tubes, violet in front and delicate green posteriorly, the latter colour being 

 due to the development of the reproductive elements. Moreover, in the feet the developing 

 heteronereid bristles can be seen. The eyes by-and-by enlarge. Peritoneal pigment is 

 absorbed and other changes occur, as already noted. He truly calls this epigamy. 

 Some, moreover, are hermaphrodite in the Nereid form, developing ova and sperms, 

 as Mecznikow found at San Remo and Villefranche-sur-mer. The colour was violet or 

 "rosy vinous." Moreover, no transformation was apparent in December, January, and 

 February. This is probably the form found by Moquin-Tandon at Marseilles, 1 though 

 the foot, as Bgured by Mecznikow, shows certain differences. So far as known it is still 

 a question whether a specimen which has borne sexual elements as a Nereid can after- 

 wards become a Heteronereid. 



Racovitza (1896) describes the structure of the cephalic lobe (brain) in this species 

 and compares it with that in certain other families. He finds three regions, viz., the 

 sincipital connected with the eyes and antenna?, the region of the palps, and the nucal 

 (posterior) connected with the ciliated nucal organs. 



Mobius (1871), in the ' Pommerania ' Expedition, observed that Nereis zostericola, 

 Heteronereis fucicola, and Nereilepas variabilis were all forms of Nereis Dumerilii. 



Wistinghausen 2 distinguishes three forms of this species : (1) In which reproduction 



1 ' Ami. Sc. Nat./ 5 e ser., t. xi, p. 134. 



2 f Mitth. Zool. Stat. Neap./ 1891. 



