﻿62 



PROCEEDINGS OP THE 



[Dec, 1856. 



time becoming rather inactive, sinking to the bottom of the jar, and 

 there remaining, and I incline to think that it may sometimes be a 

 provision for the discharge of the hard-parts of the prey at once 

 without the cavity of the bell. Yet I have seen this discharge 

 take place, with the proboscis even somewhat contracted within 

 the bell, which was in its normal position. With regard to the 

 reversion, perhaps I should rather say the inversion of the bell, 

 though I have seen specimens still somewhat active in that con- 

 dition, yet I am pretty sure that it is a sickly sign, and I do not 

 recollect any instance in which a specimen survived very long 

 after it had taken place, nor any in which the normal position was 

 resumed. Yet, it is not only in confinement that this phenomenon 

 occurs, for I have taken the animal with the dipnet so reverted, 

 and that in the midst of its breeding time, the young hydras hold- 

 ing on to the inverted bell. 



Turritopsis nutricula is a lively animal, swimming gaily about 

 near the surface of the water, with very regular rythmical pulsa- 

 tions. I have so frequently taken numbers together in the same 

 spot, that I incline to think it gregarious, like Geryonia. And 

 another circumstance of peculiar interest is, that usually, only 

 individuals of the same, stage of growth flock together. Its motion 

 in swimming is peculiar. Though it does not shoot forward so far 

 at every stroke as Sarsia, yet each throb of the disk gives it a con- 

 siderable impetus. Now, if we examine a Thaumantias or Geryo- 

 nia, or Tima, while swimming, we see it propelled by many 

 successive pulsations in a straight line, corresponding to the 

 vertical axis of the animal, but this is not the case in Turritopsis. 

 The pulsations here are slow, measured, powerful, each appearing 

 to have a more special design in it than the oft repeated pulsations 

 of Thaumantias, and each, instead of driving the animal directly 

 forward towards the points whither its whole course tends, propels 

 it in a direction crossing that line diagonally, like the course of a 

 ship in tacking or traverse sailing. It is thus propelled first to one 

 side of its course and then to the other, its actual track being a 

 zig-zag. This shows that the pulsation is not given equally by all 

 parts of the transparent bell, but that the sides alternate slightly, 

 and so produce the zig-zag motion. It, therefore, shows a tenden- 

 cy to specialization between the sides of the bell, which is an 

 approach to bilateral symmetry, not observed in other Disco- 

 phores. Analogically, also, it reminds us of the manner in which, 

 among the higher animals, especially the birds and man, the 



