7. THE BLOOD-VASCULAR SYSTEM 77 



functions of a corpus cardiacum — the accummulation of food reserves — is 

 performed by this organ. An haematopoietic function seems to be excluded 

 since its cells have never been observed to divide to form the cellular elements 

 of the blood. It is possible that the main functional significance of the corpus 

 cardiacum lies in its role as a sort of valve, allowing the blood to pass in only 

 one direction. Chink-like spaces filled with blood are frequently visible here 

 and there between its cells. These lacunae probably communicate through 

 narrow apertures in the limiting membrane both with the lumen of the 

 vessel itself and also with the lateral vessels which carry blood from the 

 dorsal vessel. One can well imagine that when the ventral vessel is wide and 

 relaxed the blood runs freely into it from the lateral vessels through these 

 chink-like gaps in the corpus cardiacum. But when the ventral vessel con- 

 tracts the cells of the corpus cardiacum are compressed by the blood pressure, 

 the lacunae between them are clenched tight shut and the blood cannot run 

 back into the lateral vessels. This hypothesis remains unproven for the 

 moment until the supposed links between these lacunae in the corpus 

 cardiacum and the lumina of the vessels have been successfully demonstrated. 

 It is possible, finally, that when waves of contraction run along the walls of 

 the ventral vessel they tightly compress the corpus cardiacum which, without 

 doubt, greatly aids the complete evacuation of the blood from the contracted 

 region, forcing it forward into the next section of the vessel which is momen- 

 tarily broad and relaxed. 



Johansson (1939) looked upon the cellular tissue in the ventral vessel as 

 the rudiments of a gut. No factual evidence, however, has been presented 

 to support this idea. 



A structure analagous to the corpus cardiacum is developed in the dorsal 

 vessel of the Thecanephria. It is situated in the very front part of the vessel 

 where it is attached to the dorsal wall. In Lamellisabella and Spirobrachia it is 

 developed to such an extent that it blocks a considerable part of the lumen 

 of the vessel in front of the renal sac (Fig. 51). 



The blood 



While working aboard R.V. Vityaz' I have repeatedly observed that in all 

 Pogonophora the blood of the living animal is red. 



[This is because the blood contains haemoglobin, Southward and South- 

 ward, 1963.] 



The blood plasma contains masses of very small unnucleated bodies [in 

 fixed and stained material]. It is doubtful from their appearance whether 

 one may legitimately interpret them as cellular elements and in sections thev 



