LEPIDOSIREN PARADOXA. 
67 
channel; this relationship is maintained in the third part of 
the bulbus where the venous stream passes dorsal to the two 
septa and so enters the posterior pair of aortic arches, while 
the arterial stream passes ventral to the septa and enters the 
anterior aortic arches (Text-fig. 1 and PL 5, fig. 4). 
Text-fig L 
Diagram of valves in the bnlbus cordis as seen from the ventral 
side. The line A indicates the course of the arterial blood, the 
line V that of the venous blood. Sp. V.p. Sj)iral valve on the 
ventral wall of the proximal part of the biilbns. SjJ. V. t. Spiral 
valve on the dorsal wall of the transverse part of the bulbus. 
Sp. V. d. Spiral valve on the right wall of the distal part of the 
bulbus. B. B. 3. Longitudinal valve on the left wall of the 
distal part of the bnlbus. 
Owing to the very small amount of musculature in the walls 
•of the middle and distal segments of the bulbus, the propulsive 
movement in those parts must be more an elastic recoil than 
an active contraction. 
Regurgitation from bulbus to ventricle will be prevented 
partly by the plugging effect that the distal end of the 
prominent valve in the proximal part must have on a back- 
