ANATOMY AND PHYSIOLOGY. 39 



ticm, 70 in the dorsal ; on the second, 64 ventral, 68 dorsal ; 

 on the third, 74 ventral, 88 dorsal ; and on the fourth, 63 ven- 

 tral, and 64 dorsal. It required 2 minutes to accomplish the 

 beats during a single oscillation. In another individual of 

 the same species, considerably larger than the former, but 

 still quite immature, there were 138 pulsations in one direc- 

 tion, and 120 in the other. Two or three of the concluding 

 beats of each oscillation were not so vigorous as the rest ; and 

 when the action was about to change, a dead pause ensued of 

 about two seconds. 



In Polyclinum aurantium the pulsations were found to be 

 112 in one direction and 115 in the other ; and on starting, 

 the beats were slow. They afterwards became rather rapid, 

 and before ceasing were again retarded : the action then 

 stopped for a second or two before recommencing in the oppo- 

 site direction. The pulsations in BotrijUoide* radiata are 

 nearly as numerous as they are in the last species. In one in- 

 dividual 102 beats were counted in the one direction, and 115 

 in the other. 



The above account of the circulation will be found to agree 

 with Dr. Lister's description of it in Perophora, so far as it 

 was determined in that form ; but that excellent observer did 

 not detect the flow of the blood through the suspenders, al- 

 though " filaments " attaching the branchial sac to the mantle 

 are described and figured by him. Their function as blood- 

 carriers seems equally to have escaped detection by Van 

 Beneden, though he must have been aware of their existence 

 as bands or ties; for they were figured by Snvigny, who de- 

 scribed them as ligaments attaching the braiichia to the inner 

 tunic,* and they are well known to anatomists generally. 

 Van Beneden, however, discovered the necessity of a passage 

 for the blood-current from the " periintestinal cavity " to the 

 branchia to prevent engorgement when the pulsations of the 

 heart were continued for any length of time in one direction. 

 He therefore believed that the required communication was 

 effected through the agency of the " respiratory tentacles "t. 



It will now, however, be of no avail to discuss the improba- 

 bility of such an opinion, since ample communications have 

 been demonstrated. But it may be remarked that these ten- 

 tacles are undoubtedly hollow, and that in each there is a 

 double channel, that the blood will assuredly pass up one of 

 them and down the other, and that it will oscillate in unison 

 * ' Memoires sur les Animaiix sans Vertebres/ pt. ii [p. 97, pi. vi, f. -i ; pi. 

 vii, f. 2]. 



t Op. cit. [on p. 31], p. 113. 



