782 PROCEEDINGS OF THE ACADEMY OF [Dec, 



series comprises T. IX to T. XVI, which follow the same plan in 

 order of appearance, T. IX following T. I, etc.,. eight numbers 

 intervening in each case (fig. 18), 



While this may seem more like a fanciful exercise of the imagina- 

 tion than an actual condition in nature, the truth is that the larger 

 the number of specimens in which one tests the arrangement of the 

 marginal organs by this rule, the more will one be convinced of 

 the remarkably constant adherence to it. Given a specimen with, 

 say, twenty -eight tentacles, such as that represented in fig. 19 — 

 this is a drawing of a specimen of Olmdias from the Bahamas, a 



Fig. 20. 



genus which follows the same rule in the order of appearance ot 

 the tentacles as Gonionema — the sense-organs are not so numerous 

 in Olindias. In this specimen the most_^recently arisen tentacle in 

 each quadrant is evidently the one numbered VII, lying just after 

 each perradial tentacle. Then, if the rule which we have educed 

 applies in this case, we should expect to find the eighth tentacle in 

 each quadrant arising in a corresponding position with relation to 

 the interradial tentacle. 



And such we find to be the case. Fig. 20 shoAvs a slightly older 

 specimen of the .'-ame species in which we plainly see the eighth 

 tentacle in each quadrant lying in its appointed place (VIII). 



