64 Reviews and Notices of Boohs, 



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 or variously curving, follow the 

 motions of the main sphere, being carried on with it in all its movements, 

 which are no doubt influenced by them to a considerable extent. 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 in the 

 direction 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 movements, 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 organiza- 

 tion of animal bodies, that parts may be elongated and contracted to 

 such extraordinary and extensive limits by means of muscular action. 

 And what is so surprising, is not so much the sudden and powerful 

 contraction which brings within the compact limits of a pin's head the 

 whole mass of these tentacles that a moment before were floating so 

 elegantly through such a great extent in the water, as the relaxation, 

 which takes place in an absolutely passive manner ; for when watching 

 them we are suddenly struck with astonishment on finding that the 

 tentacle which we expected to see drop to the bottom of the jar is still 

 in organic connection with the body from which it hangs. Plate I. of 

 my paper in the Memoirs of the American Academy represents some 

 few of the attitudes of our Pleurobrachia in its various movements, one 

 of which is reproduced in this work (PI. II". Fig. 25) ; but I cannot find 

 words to describe all the beautiful changes which the parts thus in 

 motion assume in different attitudes. At one moment the threads, when 

 contracted, seem nodose ; next, when more elongated, these knots are 

 stretched into the appearance of a spiral ; next, the spiral, elonga- 

 ting, assumes the appearance of a straight or waving line. But it is 

 especially in the successive appearances of the lateral fringes arising 

 from the main thread that the most extraordinary diversity is displayed. 



