OF THE ACALEPH,E OF NORTH AMERICA. 315 



to siicli extraordinary and extensive limits. And what is so surprising is not so 

 much the sudden 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. represents some few of the attitudes of Pleurobrachia 

 in its various movements ; 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, elongating, assumes the 

 appearance of a straight or waving line. But it is especially in the successive ap- 

 pearances of the lateral fringes arising from the main thread, that the most extraor- 

 dinary diversity is displayed. Not only are they stretched under all possible angles 

 from the main stem, at times seeming perpendicular to it, or bent more or less in 

 the same direction, and again as if combed into one mass ; but a moment afterwards 

 every thread seems to be curled or waving, the main thread being straight or un- 

 dulating ; then the shorter threads will be stretched straight for some distance, 

 and then suddenly bent at various angles upon themselves, and perhaps repeat such 

 zigzags several times, or they will be stretched in one direction, and bent at 

 various angles in the plane of another direction ; then they will be coiled up from 

 the tip, and remain hanging like pearls suspended by a delicate thread to the main 

 stem, or, like a broken whip, be bent in an acute angle upon themselves, with as 

 stiff an appearance as if the whole were made up of wires ; and, to complete the 

 wonder, a part of the length of the main thread will assume one appearance, and 

 another part another, and pass from one into the other in the quickest possible succes- 

 sion ; so that I can truly say, I have not known in the animal kingdom an organism 

 exhibiting more sudden changes, and presenting more diversified and beautiful images, 

 the action, meanwhile, being produced in such a way as hardly to be understood. 

 For when expanded, these tlireads resemble rather a delicate fabric spun with the 

 finest spider's thread, at times brought close together, combed in one direction 

 without entangling, next stretched apart, and preserving in this evolution the most 

 perfect parallelism among themselves, and at no time, and under no circumstances, 

 confusing the fringes of the two threads ; — they may cross each other, they may 

 be apparently entangled throughout their length, but let the animal suddenly con- 



