CRVPTOCHITON STELLERI MIDD. 



223 



causing its protrusion, and it is reasonable to suppose that accord- 

 ing to the state of contraction of the pedal muscles generally the 

 blood pressure of the visceral cavity may vary, causing a flow of 

 blood from the foot into the cavity or in a reverse direction. 

 Injections show that in dead or flaccid animals the line of least 

 resistance is from the pedal sinuses laterally into the kidney. 



As with the pedal nerve sinus a well-defined septum destroys 

 any communication with the head cavity (Fig. 3) but throughout 

 its entire course it is in frequent communication with the pedal 



sinus which supplies it and the adjacent regions with aerated 

 blood. 



In all of the specimens carefully examined a connection exists 

 between the pedal nerve sinus and the bases of the median pro- 

 tractor sinus (;//) so that blood may pass from one to the other. 

 Throughout its greater extent the pedal nerve sinus receives its 

 blood from the pedal sinus and it is difficult to understand this 

 peculiar anterior connection unless it is some device to aid in the 

 protraction of the anterior margin of the foot. 



