CHAPTER 7 



The Blood-Vascular System 



The Pogonophora possess a strongly developed closed blood-vascular 

 system. Two blood vessels, a dorsal and a ventral (Caullery, 1914, 1944; 

 Johansson, 1939), running the whole length of the body are connected 

 anteriorly by the vascular system of the tentacular apparatus and posteriorly 

 by lateral transverse commissural vessels. In the fore-part of the body both 

 longitudinal vessels lie in the mesenteries. Part of the ventral vessel in the 

 mesosomal region is differentiated to form a heart (Ivanov, 1955a). A peculiar 

 organ inside the ventral vessel has been called the "corpus cardiacum". 



The blood vessels 



The dorsal vessel reaches its greatest calibre near the protocoelomoducts. 

 In the Thecanephria it is particularly broad here and envelops the excretory 

 portions of the coelomoducts from below, forming around them the long 

 "renal sacs" in which they are bathed by blood on all sides. The dorsal 

 vessel is considerably narrower in front of the level of the heart, and narrow 

 vessels open into it from the ventral side, carrying blood from the tentacular 

 apparatus. 



Three parallel branches extend from the dorsal vessel into the cephalic 

 lobe where they terminate blindly. One of them — the median cephalic 

 vessel — is a direct continuation of the dorsal vessel; the other two — the 

 lateral cephalic vessels — branch off at the level of the heart (Fig. 52, Pis. I, 

 II). The cephalic vessels are joined to one another by an asymmetrical plexus 

 of transverse anastomosing vessels. The posterior ends of the lateral vessels 

 project backwards in the Athecanephria as a pair of sac-like expansions. 

 Longitudinally grouped bundles of dorso-ventral muscle fibres run in spaces 

 between the cephalic vessels and their transverse anastomoses (Pis. I, II). 



The dorsal vessel is much flattened from side to side in the region of the 

 mesosoma and takes up almost the whole space between the dorsal body wall 

 and the ventral vessel (Fig. 30). Its side walls are usually covered with 

 numerous caeca (Pis. II, III), and the ventral wall is thrown into a few 

 parallel longitudinal folds. The intima of the vessel is here covered on the 

 outside by a layer of cells, apparently a continuation of the peritoneal 

 epithelium (Fig. 49). Passing through the diaphragm the dorsal vessel be- 

 comes much narrower (Fig. 32), but in the metasoma it becomes once more 



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