Chap. HI. GENUS PLEUROBRACIIIA. 247 



a Cyclopean formation, resulting from a central combination of the specks, which, 

 in Discophora}, occupy a pei-ipheric position. 



The nature of the tubercle, or ganglion-like mass, placed between the eye-capsule 

 and the fork of the funnel, is still more problematical. This body is of larger size 

 than the black speck and its capsule, under which converge the eight narrow jiro- 

 longations of the ambulacral rows, and on the anterior and the posterior side of which 

 are seen four smaller tubercles or swellings, between which arise two ridges rapidly 

 diverging forward and backward. I can offer only suggestions respecting these 

 parts. I am, however, inclined to believe that the two ridges between the four 

 small swellings extending forward and backward are only outlines of the folds which 

 form the circumscribed area ; that the four small swellings themselves are clusters 

 of cells connected with the narrow termination of the ambulacral rows ; and that 

 the wall-like outlines of the tubercle are determined by the fork of the funnel. 

 As for nerves, which are said to arise from the ganglion connected with the black 

 speck, I have been unable to make them out. I have ti-aced the motory cells 

 which surround the abactinal extremity of the chymiferous funnel ; I have seen 

 these cells diverging from the actinal side of the so-called ganglion, but have 

 never Ijeen able to trace any one of them beyond the usual length of these cells ; 

 I have repeatedly seen these cells in a state of contraction or relaxation, pre- 

 senting so little resemblance to nerves that I think it rather assuming to ascribe 

 a nervous system to the Ctenophora^. I am even satisfied, from the descriptions 

 published, that the eight converging narrow prolongations of the ambulacral rows, 

 of which I find no mention in former authors, must have been mistaken for ner- 

 vous threads by some ; and when Professor Grant states that Beroe has eight main 

 nerves arising from eight ganglions, I suppose he alludes to some contracted cells 

 of the spherosome, or to the eight narrow abactinal bands, the connection of 

 which with the rows of locomotive flappers is so easily traced. I do not, however, 

 deny that this centre is a point where we have to look for at least one part of 

 the nervous system, and the movable margin of the mouth for the other part, 

 if there really be a distinct nervous system in Ctenophoras. But, as for myself, 

 I have fliiled in tracing it out ; though, I may add, I am sufficiently acquainted 

 with the structure of the region where it is said to have been observed, to doubt 

 the accuracy of the statements Avhicli have been made about it. And I express 

 these doubts, notwithstanding the doubts I myself entertain respecting the real 

 nature of some organs around the central black speck, for the very reason, that, 

 after finding there more than has been seen and described, and various things 

 which may answer the vague descriptions given, I do not in reality find what 

 has been said to exist in that part of the animal. 



When I first described our Pleurobrachia I did not know its mode of develop- 



