SOME POINTS IN THE ANATOMY OP POLYOH^TA. 261 



tenidae. In those three families an anterior heart similar to 

 that of the Chlorhsernidse is present, and its posterior end is 

 connected with a blood-sinus in the walls of the intestine, 

 which is the only representative of the typical dorsal vessel. 

 The intestinal blood-sinus is connected, on the ventral side of 

 the intestine (e.g. in Amphitrite Johnstoni), with a large 

 definite vessel, which at the level of the posterior end of the 

 heart divides into two branches ; these pass up one on each side of 

 the oesophagus, and unite to form the heart. Thus the paradox 

 is here true that the typical dorsal vessel is in these families 

 chiefly represented by a ventral vessel. The usual subintes- 

 tinal or ventral vessel is of course present in addition. Thus 

 Horst's remark, that the presence of a free dorsal vessel in the 

 anterior somites only is merely embryonic in Terebellidee, is 

 far from correct. Salensky, it is true, describes the arrange- 

 ment as existing in the larva of Terebella ; but he does not 

 assert that any change occurs in later development, and, as a 

 matter of fact, the arrangement is, as I have said, especially 

 characteristic of the Terebellidae, Amphictenidse, and Ampha- 

 retidse, in the adult condition. 



But the most interesting point about this heart is the cel- 

 lular body it contains. Claparede, in his 'Ann. Chet. de 

 Naples,' mentions this body in Terebella multisetosa, 

 Grube, and in Audouinia filigera. In describing the latter 

 species he says there are three brown cords in the walls or in 

 the lumen of the dorsal vessel, and similar structures are 

 common to all the Cirratulidse. Of the body in Terebella 

 multisetosa he says that the dorsal vessel contains a sub- 

 stance of a deep black colour distributed in irregular cords. 

 It is curious that Claparede should have recognised the nature 

 of the heart in Terebellidae, and not seen the similarity between 

 that organ and the heart in Chlorhsernidse. In his ( Structure 

 des Ann. Sedentaires,' 1873, Claparede figures transverse sec- 

 tions of the heart of Audouinia filigera and of Terebella 

 flexuosa, and gives a fuller account in the text of the glan- 

 dular cords seen in these sections. He says that in his pre- 

 vious work he had supposed the cardiac organ in Audouinia 



