18 THE VOYAGE OF H.M.S. CHALLENGER. 



crown, where it divided into two branches, which passed within and around the 

 tentacidar cup, and sent a twig to each of the tentacles. Along these the corpusculated 

 blood streamed, returning by a vein in each, while four large trunks passed from the 

 base of the ring (one from the inside, and another from the outside of each of the horns 

 of the ring). Each pair and afterwards the two trunks united, and then the two latter 

 coalesced to form a single large vein, which traversed the axis of the body on the opposite 

 side of the gullet to the artery. The whole of the trunks are contractile, the artery 

 pulsating about fifteen times per minute. Professor Allman, again, found that the 

 blood returned by the same channel in the tentacles — the current being thus alternately 

 forward and backward ; and in the examples from the Challenger only one distinct 

 trunk is visible. D)'ster describes the blood as ascending some tentacles and descending 

 others. The pulsations occur only in the artery, whereas in the vein the current is 

 continuoiis, and the main trunks are connected by numerous branches. Schneider 

 regards, after Krohn and Claparede, the vessels just alluded to as dorsal and ventral ; 

 and he makes the statement (which has not been confirmed) that the red blood- 

 corpuscles in the young form float freely in the body-cavity, and then enter the vessels 

 at the base of the tentacles. In a note on the British species, KoUiker gives the size of 

 the nucleated and intensely red blood-corpuscles as '004-0 "005, and mentions also 

 colourless amoeboid cells and yellowish corpuscles. Dyster gives the diameter of the 

 corpuscles in his species as l-3200th to l-1700th in., and about l-8000th of an inch in 

 thickness ; while Kowalewsky estimated them as about four times the size of those in 

 man. 



Nervous System. 



In the preliminary account no observations of note were made on the nervous 

 system, but the subsequent appearance of Mr. Caldwell's paper in the Proceedings 

 of the Royal Societ}^ again directed attention to the subject, though, from the imperfect 

 preservation of the specimens collected both by the Challenger and Dr. Haswell, 

 considerable difficulties were met with.' 



Mr. Caldwell observes ' that " nervous processes of the ectoderm cells retain their 

 connection with the ectoderm, and concentrations, both of fibres and ganglion-cells, 

 occur in the skin outside the homoQ;eneous basement-membrane. The central nervous 

 system remains therefore in the epidermis, representing the primitive condition. 



" Concentrations of the nervous system take place round the mouth to form a 

 postoral nerve-Hng. The anus lies outside this. The ring follows the line along the 

 base of the tentacles, and has therefore, like them, the form of a horse-shoe. In front of 



* Dyster could detect no distinct nervous system, " though it is possible two obscure organs at the posterior part 

 of the floor of the lophophore may be oesophageal ganglia." The animals showed no sensibility to light. 

 2 Proc. Roy. Soc, vol. xxxiv. p. 372. 



