Chap. III. GENUS PLEUROBRACHIA. 205 



l^arallel, 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 comjolication of that structure, or 

 the delicacy of the colors and hues, which, Avith 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 inilike 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 vmdulations. And though I have 

 found contractile fibres in these thin threads, showing that these movements are 

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

 that parts may be elongated and contracted to such extraordinary and extensive 

 limits by means of muscular action. And Avhat 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 ele- 

 gantly through such a great extent in the water, as the relaxation, which takes 

 place in an absolutely passive manner ; for when Avatching them we are suddenly 

 struck with astonishment on finding that the tentacle Avhich we expected to see 

 drop to the bottom of the jar is still in organic connection Avith the body from 

 Avhicli it hangs. Plate I. of my paper in the Memoirs of the American Academy 

 represents some fcAV of the attitudes of our Pleurobrachia in its various movements, 

 one of AA'hich is reproduced in this Avork (PI. IP. Fig. 25) ; but I cannot find Avords 

 to describe all the beautiful changes Avhich the parts thus in motion assume in 

 different attitudes. At one moment the threads, Avhen contracted, seem nodose ; 

 next, Avhen more elongated, these knots are stretched into the appearance of a 

 spiral ; next, the spiral, elongating, assumes the appearance of a straight or Avaving 

 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. 

 Not only are they stretched under all possible angles from the main stem, at times 



