54 DISCOPHOR^. Part III. 



with one another, and as the ambulacral tubes, which are homologous to the radi- 

 ating chambers of the Polyps, alternate with the ovaries in their radiating arrange- 

 ment, so do we find here the radiating genital system, with its peripheric radiating 

 tubes, alternating with systems of radiating tubes extending directly to the main 

 cavity of the body. It seems therefore justifiable to call the radiating system of 

 chymiferous tubes, corresponding to the angles of the mouth, the ambulacral system 

 of tubes, and those which alternate with them, the interambulacral or genital system 

 of chymiferous tubes. 



It thus appears that the peculiar symmetry of our Aurelia arises from the fact 

 that the ambulacral system of chymiferous tubes is comparatively small and simple, 

 alternating with an interambulacral system of chymiferous tiibes, expanding into 

 broad pouches, from each of which arises a wide system of peripheric tubes. It 

 appears further, that the main branch of the interambulacral, as well as that of the 

 amljulacral system, terminates at the base of an eye, while the main lateral branches 

 of the interambulacral system, which are also simple, correspond to much less marked 

 indentations of the margin in which there are no eyes, but which Ehrenberg has 

 considered as marking the position of as many marginal, anal apertures. Having 

 injected a great many of these animals in a perfect state of preservation, without 

 ever perceiving an escape of the injected colored fluid at these places, and having 

 watched for days and days the circulation of the nutritive fluid through the whole 

 of these systems of radiating tubes, I venture positively to deny the presence of 

 any aperture in the periphery of these systems of parts. The lumen of these 

 simple tubes being somewhat larger than that of the adjoining branching tubes, 

 their anastomoses with the marginal tubes constitute somewhat wider spaces, in 

 which occasionally an accumulation of undigested minute particles may be observed ; 

 but these are always after a while carried along with the circulation, and are brought 

 back to the central cavity in the returning currents, and finally rejected through 

 the oral aperture. PI. VII. Fig. 5, in which parts of the genital pouches and all 

 the oral appendages have been removed, shows distinctly that while the interam- 

 l)ulacral radiating tubes arise from the periphery of the genital pouches, the ambu- 

 lacral tubes extend to the main cavity of the body. Ehrenberg seems to have 

 overlooked this difference, for he represents (PI. I. Fig. 1, and PI. III. Fig. 5, of his 

 paper in the Transactions of the Berlin Academy for 183G), in an injected speci- 

 men, all the radiating tubes as arising from one common cavity, which is certainly 

 not the case in the AureUa flavidula. 



In px'oportion as our species grows older, the anastomoses of the radiating 

 tubes become more numerous along the margin, and the circular marginal tube 

 loses gradually its character of a continuous tube, and assumes more that of a 

 net-work of anastomoses, with which communicate the many marginal tentacles. 



