170 BULLETIN OF THE 



in the young of Cyanea. In Aurelia, Plate VII. fig. 6, thcv are represented by 

 •wart-like excrescences of small size, covering the whole upper surface of the 

 bell, even to the marginal lobules. 



On the Sense Organs found on the Bell Margin of 

 Cyanea arctica. 



The structure of the sense organs found in the rim of the bell of Pelagia, 

 Aurelia, and Cyanea has been carefully studied by Dr. Eimer. His observations 

 of Cyanea are less complete than of the other genera, and as the differences are 

 in some respects so radical, I have here described the more important details 

 of their anatomy again. The "marginal sense bodies " of C. arctica are eight in 

 number, and are situated at equal distances on the rim of the umbrella in in- 

 cised angles, slightly removed from the margin. Morphologically, each of these 

 structures is a modified tentacle, as pointed out by Agassiz. 



The eight extensions of the stomach in the intei"val between the lower sur- 

 face of the umbrella and the lower floor are separated from each other by verti- 

 cal partitions connecting these structures. The early condition of these vertical 

 partitions has been already mentioned in speaking of the ephyra. It remains 

 to be noticed that thej^ lie in radial lines, separating the octants which bear the 

 sense bulb from those from which the bundles of marginal tentacles hang. 

 The chymiferous tubes or extensions from the stomach into the periphery of 

 the disk divide as they approach the margin of the umbrella into a single small 

 central, and two large lateral branches. The central of these, which is medially 

 placed, extends directly into the otocyst, while the lateral divisions are subdivided 

 into many dendritic branches, becoming more and more subdivided as they ap- 

 proach the margin of the lobes on either side of the sense bulb or otocyst. It 

 will be seen, however, by a consultation of the figures, Plate VII. figs. 7, 12, 

 that only a part of the lobes adjacent to the sense bulb is penetrated by branches 

 from the optical extension of the stomach, part of which passes into the otocyst. 

 By far the greater number of dendritic branches arise from chymiferous 

 tubes, which lie in the same sector as the bunch of marginal tentacles. The 

 dendritic branches of the main divisions of the ocular tube are of two kinds, 

 one of which spreads itself out in the margin of the umbrella, while the other, 

 arising from the sides of these tubes, extends into curtain-like folds (Plate VII. 

 fig. 12 c) on the under surface of the umbrella. These curtains are placed as fol- 

 lows. On the aboral side of the adult Cyanea the otocyst is covered and pro- 

 tected by a roof-like prolongation of the upper surface of the imibrella into 

 what is known as the hood (Plate VII. fig. 12', d). On the oral side, this hood 

 does not exist in the same form. It is, however, represented in the oral cur- 

 tains. When one carefully examines the otocysts from below, or from the oral 

 side, they are found to be protected by raised walls or curtains, which do not 

 join each other, but arise from the edges of the adjacent lobes and extend par- 

 allel with each other from the base of the otocyst to a distance far beyond 

 its distal end. They are so placed in reference to each other that their free 

 edges, which are crescent-shaped, slightly overlap (Plate VII. fig. 12, c). It 



