Chap. III. ABACTINAL SYSTEM OF CYANEA. 91 



SECTION II. 



THE ABACTINAL SYSTEM OF CYANEA. 



It has already been shown, in the preceding chaptei-, that the so-called umbrella 

 of the Discophorse represents the abactinal system of the Radiates generally, and 

 more particularly corresponds to the aljactinal area of the Asterioids, since in these 

 the actinal area is stretched out in one plane with the mouth or actinostome, as 

 in the Medusae proper. 



A view of the disk from above (PI. V.) shows plainly that the whole body of 

 Cyanea is symmetrically divided, along its margin, by eight deep indentations into 

 eight identical parts, each of which shows again two minor emarginations. The 

 edge of each of these eight equal parts is thus divided into four lobes, two smaller 

 ones in the middle, and two broader ones, of which there is one on each side of 

 the smaller. Such an eighth part of the whole disk appears circumscribed by lines 

 easily seen from above, reaching an inner circle, the interior of which is divided 

 into unequal small fields. The lines which indicate the separations of the eight 

 equal parts converge from the deep emarginations to the inner circle and other 

 lines, passing between the two smaller middle lobes, and also reaching to the inner 

 circle, subdivide each eighth of the body into symmetrical halves. Thus the whole 

 disk is divided into sixteen equal parts, in such juxtaposition that two and two 

 form an eighth of the whole. Besides these straight lines, there are, nearly upon 

 the middle of each of these sixteenths, other lines running, in a somewhat crooked 

 course, from the smaller emarginations, between the larger and smaller lobes, inward 

 toward the inner circle, which they, however, do not reach. These bent lines are 

 broader toward the centre than toward the circumference. There appear, also, at 

 some distance from the edge, and facing the large emarginations, broken lines 

 extending from one crooked line to another, the angular projection of which is 

 turned toward the centre. Similar broken lines, but shorter, more waving, and 

 nearer the margin, exist also in front of the lesser emarginations, between these 

 and the eyes. In order to be able to designate these different outlines with more 

 precision, and without circumlocution, I propose to call the .short radiating lines 

 between the deep emarginations and the inner circle, the short junctions, and the 

 longer radiating lines, extending from the small emarginations to the inner circle, 

 the long junctions. These names are justifiable inasmuch as they do not desig- 

 nate lines marked on the surface, but indicate the points where the long side and 

 the short side of each sixteenth segment of the disk unite with the corresponding 



