ANATOMY AND PHYSIOLOGY. 37 



evitably take place in the pallia! plexus when the heart pul- 

 sates in the direction of the viscera ; and when its action is 

 reversed, exhaustion would ensue in this portion of the system. 



Now, though the branchial sac is attached to the walls of 

 the pallia! chamber in front and behind and along by the 

 dorsal margin, it is necessary that the lateral or reticulated 

 portions of the organ should be suspended, and in such a 

 manner as to leave a considerable space between the sac and 

 the pallia! walls. Consequently a number of suspenders are 

 provided, which,, while they retain the branchial sac in its 

 proper position, allow the required space. These suspenders 

 are in the form of cylindrical bands or ties, and are con- 

 tractile ; they pass from the transverse branchial channels 

 and from the great ventral channel to the walls of the pallia! 

 or respiratory chamber ; they are hollow or tubular, and are 

 the means of communication between these blood-channels 

 and the pallial plexus of both sides, and also Avith the visceral 

 plexus of the left side. Thus the blood-currents in every 

 part of the organism are brought under the influence of the 

 heart. One of the suspenders,, larger than the rest, connected 

 with the ventral branchial channel,, opens into a considerable 

 channel or sinus in the mantle in which the nervous ganglion 

 is placed; and the vessel which carries the blood from 

 the heart to the great branchial channel has also much 

 the character of a suspender. 



There can be no doubt whatever of the fact that the 

 branchial suspenders are tubular, and that they carry the 

 blood, as above stated, from the branchial network to the vis- 

 ceral and pallial plexuses. I have seen in several instances 

 the channels in the suspenders gorged with blood-corpuscles, 

 as well as the channels connected with them in the pallial 

 and visceral plexuses, and the transverse channels of the gill- 

 sac ; and thus by such natural injections the fact has been 

 demonstrated over and over again. And, moreover, I have 

 witnessed blood-corpuscles pass through the channels in the 

 suspenders in young living individuals of Ascidia sordida. 



When the heart acts in the direction of the dorsal ex- 

 tremity, the blood will at once be thrown into the dorsal 

 branchial channel, and will pass by the dorsal trunk of the 

 compound vessel into the test; all the transverse channels of 

 the branchial sac will be filled; and through the agency of 

 the suspending tubules or vessels the pallial plexuses of both 

 sides of the mantle, as well as the visceral plexus of the left 

 side, will be supplied in all directions ; while that portion of 

 the blood-current which is retained in the vascular reticu- 



