THE CIRCULATION OF BODY FLUIDS in 



capillaries. And it is an experimental fact that the blood- 

 pressure in the arterial system of the Cephalopod is much 

 higher than in that of the fish. The aortic pressure 

 of the octopus has been determined by several observers, 

 first by Fuchs, who found that it varied between 25-80 mm. 

 Hg ; probably the latter figure is more representative. But 

 the efficiency of the mechanism becomes even more striking 

 when the relation between the rhythm of the branchial hearts, 

 of the systemic hearts, and of the respiratory movements is 

 studied. The pulsation of the branchial hearts precedes 

 that of the systemic hearts, but at the same rate (about 30 beats 



L. Aurfcle 

 Ventrfcle 

 Fig. 28. — Heart of Cephalopod. 



per second), and the frequency of the heart-beats is almost 

 identical with that of the respiratory movements. The means 

 by which this synchronism is maintained is a fascinating field ; 

 and several investigations have been made into the innerva- 

 tion of the cephalopod heart, notably, with modern methods, 

 by Carlson and by Fry. The later work of H. Fredericq 

 provides the clearest account of the co-ordination of cardiac 

 rhythm in this group. Fredericq 's experiments were carried 

 out on the octopus, and deal with the relation of the branchial 

 and systemic hearts. When the ventricle is cut off from the 

 auricles by a ligature, the ventricular beat ceases immediately. 

 This apparently is not due to a severing of the functional 

 continuity of the conducting tissue, if any, as in the case of 



