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PROCEEDINGS OF THE 



[April, 1857. 



them. To injury of this kind, I refer also the premature fall of 

 the medusa-buds already mentioned. This circumstance gave 

 me an opportunity, however, of observing what I believe has not 

 been observed before ; viz: that 'among the marginal tentaculiform 

 individuals, when the longer ones are shed, the small ones imme- 

 diately grow out, and in three or four days, according to their state 

 of advancement, acquire equality with the longest of the original 

 circle. I have observed this fact on both the occasions when I 

 had these animals under examination. 



I should here mention that this community is not merely pas- 

 sive and floating, nor is activity confined to the central polyp, but 

 each of the three classes of individuals has its own peculiar kind 

 and range of motion, and this is pretty actively kept up by each 

 when the community is but little injured. The motion of each 

 class also is independent, as to time, of the motion of any other 

 class, considering the central polyp as the sole representative of 

 its class. These motions, in the case of the two other classes, 

 may be performed either by any individual singly, or (as, accord- 

 ing to my observation, is rather oftener the case,) by all the indi- 

 viduals of each class together. The motion of the marginal tentac- 

 uliform individuals is a vertical one, the whole bending down ver- 

 tically together, as mentioned by Guilding; but it is to be observed 

 that, in this motion, there is no longitudinal contraction, but that 

 the individual, remaining outstretched, sways downward with a 

 motion somewhat resembling that with which one of the digestive 

 polyps of Hydractinia, slowly sways itself from side to side. The 

 medusa-bearing polyps, on the other hand, have a worm-like move, 

 ment of contortion also, which is executed by each individual in- 

 dependently of the rest. But the individuals of this class have 

 also a common motion, which I have at times observed to have a 

 sort of rythmical relation between its successive acts, and I am in- 

 clined to think, that in a wholly uninjured community, this mo- 

 tion will be found to be kept up with but little cessation. It con- 

 sists in an alternate elongation and contraction of the polyps in a 

 vertical direction, which is executed synchronously by all of them, 

 "and with a sort of jerk, which distinguishes it from the elongation 

 and contraction of the central polyp. 



The months in which this Porpita has been found are June and 

 September. At both times the fall of colored particles occurred, 

 but it was only in June that their condition was examined, and the 

 result was the imperfect medusa-bud described above. They 



