314 COINTRIBUTIONS TO THE NATURAL HISTORY 



a time almost immovable, with a slight waving of some of its vibrating fringes, which 

 gentle motion easily counterbalances the difference in sjjecific gravity between these 

 animals and the water in which they live. So Pleurobrachia may appear at times, 

 and so it even does appear when it moves in its state of contraction. But generally, 

 when active, it hangs out a pair of most remarkable appendages, the structure and 

 length and contractility of which are equally surprising, and exceed, in wonderful 

 adaptation, all I have ever known among animal structures. Two apparently simple 

 irregular, unequal threads will hang out from two opposite points on the sides of 

 the sphere. Presently they will elongate, equal in length the diameter of the sphere, 

 presently surpass it, increase to two, three, five, ten, twenty times the diameter of the 

 body, and more and more ; so much so, that it would seem as if these threads had the 

 power of endless extension and development. But as they lengthen, they appear more 

 complicated. From one of their sides other delicate threads shoot out like fringes, form- 

 ing a row of beards, like those of the most elegant ostrich feather, and each of these 

 threads itself elongates till it equals in length the diameter of the whole body, and bends 

 in the most graceful curves. These two long streamers, stretching out in straight or 

 undulating lines, sometimes parallel, then diverging, follow the motions of the main sphere, 

 being carried on with it in all its movements. Upon considering this wonderful being, 

 one is at a loss which most to admire, the elegance and complication of that structure, or 

 the delicacy of the colors and hues, which, with the freshness of the morning dew upon 

 the rose, shine from its whole surface. Like a planet round its sun, or, more exactly, 

 like the comet with its magic tail, our little animal moves in its element, as those larger 

 bodies revolve in space, but unlike them, and to our admiration, it moves freely in all 

 directions ; and nothing can be more attractive than to watch such a little living comet, 

 as it darts with its tail in undetermined ways, and revolves upon itself, unfolding and 

 bending its appendages with equal ease and elegance, at times allowing them to float for 

 their whole length, at times shortening them in quick contractions, and causing them 

 to disappear suddenly, then dropping them, as it were, from its surface, so that they 

 seem to fall entirely away, till, lengthened to the utmost, they again follow the direc- 

 tion of the body to which they are attached, and with which the connection that 

 regulates their movements seems as mysterious as the changes are extraordinary and 

 unexpected. For hours and hours I have sat before them and watched their move- 

 ments, and have never been tired of admiring their graceful undulations. And though 

 I have found contractile fibres in these thin threads, showing that these move- 

 ments are of a muscular nature, it is still a unique fact in the organization of animal 

 bodies, that by means of muscular action parts may be elongated and contracted 



