On the Pccired Dorsal Vessel of Certain Eartliioorms. 425 



sented in the Oligochoita limicola ; in later stages of develop- 

 ment these two rudiments get nearer together, and finally 

 coalesce on the dorsal median line of the intestine. Vejdovsky 

 has pointed out in this paper that the developmental history 

 of the dorsal vessel in Criodrihcs seems to have some signi- 

 ficance, because it is known that the dorsal vessel of Hermella 

 is persistently double. The anatomy of this worm, especially 

 the circulation, has been described by De Quatrefages^ in a 

 beautifully illustrated memoir ; the dorsal vessels — together 

 homologous with the unpaired vessel of other genera — retain 

 their distinctness throughout the greater part of the body, 

 though connected here and there by transverse vessels ; at 

 the junction of the cesophagus with the crop the two trunks 

 unite and form a single vessel, which runs along the 

 cesophagus to the anterior end of the body. De Quatrefages' 

 figures are repeated in the illustrated edition of Cuvier's 

 " Eegne Animale," which contains figures of the circulatory 

 system of other Polychaetous Annelids ; in several of these the 

 dorsal vessel resembles that of Hermella in being double ; in 

 Terehella conchilega (PL Ic, Fig. 1) the two dorsal trunks lie 

 quite at the sides of the intestine as they do in Hermella, 

 but unite to form a single vessel at the junction of the 

 cesophagus with the intestine; in Eunice sanguinea (PL la, 

 !Fig. 2) the dorsal vessel is double, but differs in that the two 

 trunks are placed close together, apparently almost in contact, 

 on the dorsal side of the intestine ; on the oesophagus the vessel 

 is single. Dr Macintosh, in his elaborate memoir on the 

 structure of Magelona,'^ and also in a special notice of the 

 vascular system of the same Annelid published in a recent 

 volume of the Journal of Anatomy,^ has described a dorsal 

 vessel which is formed of two distinct and separate tubes 

 placed close together as in Etcnice, only divided by a narrow 

 septum : in the anterior part of the body, as in all the other 

 genera referred to, the two trunks unite. In the cases just 

 mentioned, it is interesting to note that in the " Sedentary " 

 Annelids, the two dorsal vessels resemble the two nerve 



1 Ann. Sci. Kat, ser. 3, t. x., i»l. ii., fig. 1. 

 - Zeitschr, f. wiby. Zool. , Bd. xxxi. 

 3 Vol. xiv. 



