BODY FLUIDS AND CIRCULATION 



93 



Invertebrates. In cephalopods, which have closed circulatory systems, 

 blood pressures are high, greater than those of many cold-blooded verte- 

 brates. In Octopus pressures in the cephalic artery range from 48-60 mm 

 Hg, and in one large animal reached 88 mm Hg. Differences between 

 systolic and diastolic pressures usually lie around 10 mm Hg, but may 

 attain 25 mm. In the gill veins blood pressures fall to 5-4-6-1 mm Hg; 



Fig. 3.1. Diagram of Sympathetic Pathways in a Teleost Fish 



a, artery; c, chromatophore ; ma, mesenteric artery; mrc, mixed ramus communicans; 

 pr.gn, pre-ganglionic neurone; o, oviduct; sg, sympathetic ganglion; sb, suprarenal 

 body; da, dorsal aorta; e, gut; pgn, post-ganglionic neurone. 



pulse pressure here is small, around 0-8 mm Hg. Cephalopods are the 

 largest and most active of invertebrates, with correspondingly high 

 metabolic levels (121). 



In contrast, pressures in the vessels of sluggish polychaetes are very 

 low. In Neanthes pressure in the dorsal artery is 1-1-2-2 mm Hg when the 

 animal is at rest, and increases to 17-6 mm Hg during activity (Zucker- 

 kandl in Prosser) (108). 



