﻿OF THE ACALEPH.E OF NORTH AMERICA. 243 



its bulb to be, even though its being an organ of vision should be denied, — that the 

 sensitive bulb is so closely connected with the marginal tentacles and the chvmiferous 

 tubes, and is placed in such a radiating position along the margin of the animal, as 

 to form an apparatus unparalleled in the animal kingdom. 



The tentacles of the margin (Plate V. Fig. 2, 4, 11, /,/,/, /; Plate IV. Fig. 1, 2) 

 have a structure very similar to that of the proboscis. They likewise consist of con- 

 tractile cells, and also have cells of a peculiar character upon their external surface ; 

 but the degree of contractility is far greater in these tentacles, for thev can shorten 

 to a length considerably less than the diameter of the body, and extend to four or 

 five times that length; and the quickness with which they retract and extend is most 

 astonishing. These tentacles are hollow, and the liquid which circulates in the circular 

 tube penetrates into their cavity up and down. They are gradually attenuated and nearly 

 cylindrical when extended, but rather thick when contracted. There is not the slightest 

 indication of an aperture or puncture at their end, through which fluid might be absorbed, 

 or refuse matter from the chvmiferous system rejected, nor is there any such opening in 

 anv part of the circular tube or of the other tubes through which the liquids are 

 circulated. 



The external surface of the tentacles (Plate V. Figs. 11, 12, 15, 16, 17; Plate IV. 

 Figs. 1,2) appears rough, granular, or rather tubercular; and, when elongated, these 

 tubercles are sufficiently distinct to appear like rows of beads hanging loosely to several 

 threads twisted together. But in their contracted state they come so close together, that 

 the whole surface of the tentacle appears tubercular. Upon close examination, these 

 tubercles are found to consist of heaps of minute epithelial nettling cells, arranged in the 

 form of rosettes or mulberries, each of which contains within itself a thread coiled in a 

 spiral, which may be thrown out like the threads of all nettling cells, and is provided at 

 its base, or at the upper portion of the bulb formed by the cell, with a double hook. Sim- 

 ilar cells occur, not onlv upon all the marginal fringes of the discophorous Medusae, but 

 even upon the tentacles of the margin of their mouth. I have, however, suppressed in 

 this paper the graphic illustrations of their structure which I had prepared, having since 

 discovered a highly complicated structure in similar apparatus in Polvpi. which leads me 

 to suppose that the structural details hitherto recognized in the nettling apparatus of 

 Medusae do not exhaust the subject. I foresee, indeed, that there are material additions 

 to be made to what has just been mentioned, as soon as another opportunity is afforded 

 to examine specimens of this animal. But whether their structure shall be found more 

 complicated than it is at present supposed to be, or not, so much is certain, that the net- 

 tling cells, forming the bead-like granules upon the tentacles of Sarsia, throw out, under 



