I 



Anterior Segments 0/ Ampharetidae. 471 



the last segments of the abdomen. As to the curvatm-e of the 

 palege, it is equally variable in individuals according to their 

 place of origin. The anterior segments, then, are quite 

 homologous in the Ampharetidte ; there remains the question 

 of the branchiae. Are tliese appendages borne bj different 

 segments according to the species ? May one segment bear, 

 sometimes one, sometimes two, three, or even four pairs of 

 branchiffi ? The anatomy of tlie circulatory apparatus will 

 furnish us with an answer. 



In Ampharetes Gruhei the branchiae appear to be thus 

 arranged : — three pairs on the fourth segment, which also 

 carries the paleee ; one pair on the fifth segment (first seti- 

 gerous segment). The branchiae receive the blood of the 

 heart by a distinct vessel. The heart gives off four vessels 

 on each side. This is a presumption in favour of the opinion 

 that a pair of branchiae exists for each segment, but is not a 

 proof. This proof we shall find in the disposition of the 

 efferent vessels. In fact, if we examine the ventral vessel 

 from before backwards, we see that this vessel bifurcates in 

 front into two branches going to the oesophagus ; behind this 

 bifurcation it gives off on either side a transverse branch 

 which goes to the first branchia. This vessel arises from the 

 ventral vessel in the fourth segment, in front of the diaphragm 

 which separates the fourth segment from the fifth. Tlie 

 fourth pair of branchije, in spite of its apparent insertion 

 on the fifth segment, really belongs to the seventh by the 

 origin of its efferent vessel. But here a complication presents 

 itself; this efferent vessel, on leaving the branchia in front 

 to reach the ventral vessel, anastomoses with a great lateral 

 trunk, which stretches along the whole length of the animal 

 from the seventh segment as far as the posterior segment. 

 This trunk is formed by a series of anastomoses passing from 

 one parapodium to another. The blood, returning from the 

 fourth branchia, passes in small quantity only to the ventral 

 vessel, the major portion of it being thrown into this aua^to- 

 motic trunk. The first branchia is that of the middle of the 

 anterior row, the second is the most external of the same 

 row, the third is the most internal, and the fourth is that of 

 the second row, situate just behind the first. In Amphicteis 

 the study of the circulation demonstrates equally that the 

 branchiai belong to the fourth, fifth, sixth, and seventh seg- 

 ments. The fourth branchia communicates in Ampharetes 

 with a lateral anastomotic trunk; but the heart only gives 

 origin to three trunks on each side. The first of these trunks 

 bifurcates to supply the first two branchiae, as Wiren has 

 already figured it * ; and it is this which has led this author to 

 * Wiren, ' Our Cirkulatious- och Digestions-Organen,' 1886. 



