260 J. T. CUNNINGHAM. 



others saw that the organ was a heart, and were unaware that 

 it contained a glandular body. 



Dr. Horst found that in Brada, as in Serpulidse, Ammo- 

 charidse, &c, there is a blood sinus round the intestine, and 

 the heart is continuous with this sinus, and therefore a true 

 dorsal vessel, through which the blood is conducted from the 

 walls of the intestine to the gills. It is to be remarked that 

 this is a confirmation of the account given by Quatrefages in 

 ' Hist, des Anneles/ 1865, i, p. 54. Max Miiller, on the 

 other hand, supposed the posterior end of the heart to be 

 blind. Dr. Horst then points out the agreement between the 

 arrangement described by him in Brada and that described by 

 Vejdovsky in the Enchytrseidse, which also possess a dorsal 

 vessel only in the anterior somites, its place being supplied 

 posteriorly by a blood-sinus in the wall of the intestine ; and 

 further says the researches of Salensky on the development of 

 Terebella ('Arch, de Biologie,' t. 4) have shown that such an 

 arrangement is in other Annelids only embryonic. 



I have examined the vascular system in Trophonia 

 plumosa, and although I find Horst' s statements for the 

 most part correct, there is one feature which he does not men- 

 tion which might give rise to another explanation. There is, 

 namely, a thin vessel running in the dorsal median line on the 

 inner surface of the body wall, unaffected by the convolutions 

 of the intestine, receiving metamerically arranged transverse 

 vessels from the walls of the latter, and opening into the 

 dorsal side of the heart at a point a third of its length from 

 the hinder end (see fig. 17). It is thus a question which 

 represents the typical dorsal vessel — this separate vessel that I 

 have described, or the blood- sinus in the walls of the intestine. 1 

 am inclined to think the former, and that the posterior end of 

 the heart may be taken as representing a vessel passing from 

 the intestinal blood-sinus to the dorsal vessel, while the ante- 

 rior end of the heart is the direct continuation of the dorsal 

 vessel. These relations are shown in fig. 17. 



However this may be, the thin dorsal vessel mentioned above 

 is not represented in Terebellidse, Ampharetidee, and Amphic- 



r 



