44 



ACALEPHAE. 



the other. They then terminate in another tances, a circular vessel, which passes corn- 

 annular vessel, which surrounds the mouth, pletely round the circumference of the animal. 

 In their course they give off numerous Four of the radiating vessels correspond with 

 branches. From the oral circle of vascular the four fleshy pillars of the process supporting 

 structure arise two large vessels, which run the arms, and there exists on the internal sur- 

 along the walls of the gastric cavity, and ap- face of each of these pillars, a groove, which 

 pear to unite with the other circle at the anal establishes a direct communication between the 

 extremity. These last Eschscholtz regarded as corresponding vessel, and one of the large 

 veins, and the eight external vessels as arteries, vessels of the central process. The other 

 He supposed that the veins, passing along twelve are distributed by threes in the intervals 

 the walls of the stomach, absorbed the nutri- between the first four, and arise from those 

 ment, and then carried the circulating fluid to parts of the stomach which are closed by the 

 the cilia for aeration. In the course of his plaited membranes. The space intervening 

 observations on the Beroe ovatus, Dr. Fleming* between the circular vessel and the margin of 

 distinctly saw a fluid moving " backwards and the disc is occupied by an innumerable multi- 

 forwards" in the external vessels ; and he states tude of little vessels which form a net-work 

 that " while the animal was active, there were like the finest lace.* In medusa aurita, there 

 numerous small spaces in the different vessels are also sixteen radiating vessels, four of which 

 where the contained fluid circulated in eddies." arise from each of the four sacs, into which the 

 Dr. Fleming failed to detect any structure in gastric cavity in this species is divided. Two 

 the vessels which could produce these partial of the four vessels in each group are simple, 

 motions. In cesium naiadis, Eschscholtz thought the other two are several times bifurcated ; 



that he saw the system of vessels more dis- 

 tinctly than in any other of the acalephae. He 

 thus described it : " From the base of each of 

 the two tentacules, a vessel takes its rise, and 

 goes towards the bottom of the stomach. Here 



both the simple main trunks and all the 

 branches so formed, enter a circular vessel sur- 

 rounding the disc, which seems to be connected 

 also with the tubular cavities of the numerous 

 cilia which surround the margin like a fringe, 



the two vessels unite, and form a little vascular and which are capable of elongation and con- 

 circle around the water-canal (intestine). From traction.-)- Carus remarks with regard to the 

 the upper margin of this circle, four straight circular vessel, that " it may be considered as 

 vessels arise, which go towards the two rows of an extremely simple rudiment of the great ctr- 

 cilia-bearing organs placed on the dorsal sur- culation of superior animals, in case we view 

 face. Under these they run, two in one di- the radiating as chyliferous vessels.";}; 

 rection, and two in the other. At either V. Respiration. It is probable that the air- 

 extremity of the body, these unite with certain bladders of the physograda, the swimming 

 vessels running superficially along the sides, organs of the diphyda, and the cilia of the 

 and which complete the circulation by entering ciliograda are all subservient, in a greater or 

 the first set of vessels just before they begin to less degree, to the respiratory function, as well 

 run beneath the ciliated organs. All these as to locomotion. The vessels in the last men- 

 vessels are simple canals, of the same diameter tioned class, which have been described above 

 throughout, without any visible branches. They as appertaining to the circulating system, are 

 contain a colourless watery fluid, in which mi- regarded by some as respiratory organs ; and 

 nute yellowish globules are seen to move. In by Lamarck were compared to the tracheae of 

 the vessels which arise from the bases of the insects. They have been called aquiferous 

 tentacules, the globules mount upwards ; they trachea. Those who consider them in this 

 assume a rotatory motion in the vascular circle; light believe that they are open at two points, 

 and, in the four dorsal vessels, they seem to so as to admit the circumambient fluid to pass 

 move, some in one direction, others in the other, freely through them. The most recent and 

 It is probable that what appears to the eye as accurate observations, however, leave it doubt- 

 one vessel, is, in reality, composed of two ful whether this really takes place in the 

 vessels, running parallel and close together."f ciliograde acalephae. 



Seeing that the radiating vessels which arise With regard to the pulmograda, several 

 from the gastric cavities of the pulmograda parts and organs have been pointed out by 

 seem to carry out the nourishing material to all different observers as being, in all probability, 

 parts of the body, and that they are, in some the seats of the respiratory function. Cuvier 

 species at least, connected with other vessels thought that the delicate plaited membranes 

 which form a complete circle, we are disposed which exist between the fleshy pillars of the 

 to class them under this head along with the central process in rhizostoma, and which form 

 vascular structures already described. The in part the walls of the stomach, might be re- 

 exact analogies of their functions, however, garded as the organs of respirarion. Eisenhardt 

 have not yet, we conceive, been distinctly supposed that he saw them in certain tentacu- 

 made out. lated processes attached to the membranous 



From the stomach of rhizostoma, formerly partitions which divide the gastric sacs of some 



described, sixteen vessels arise, and pursue a species from one another ; while Gaede looked 



straight course outwards to the margin of the upon the four small sacs which overlie the 

 disc, near which they all enter, at equal dis- 



* Mem. Wern. Soc. iii. 401. 

 t Op. cit. p. 14. 



' Cuvier, Journ. de Phys. xlix. 438. 

 t Gaede, Anat. der Medusen. 

 t Carus, Comp. Anat. (by Gore,) ii. 266. 



