204 CTENOPHORiE. Part II. 



on o])po8ite sides, which may Ijc observed, during the whole summer, along the 

 shores of Massacliusetts and Maine, and, further north, to the shores of Greenland. 



Tlie Ctenophoraj differ essentially from the Discophorw. Both their form and 

 organs of locomotion give them a different appearance. The Discophor», setting 

 aside the various modifications arising froni marked peculiarities of their outline, 

 move like an umbrella, which, by alternately o2iening and shutting, would make its 

 wa_\" under water by means of such movements. It is by the contraction of the 

 1)0(1}' alone, or rather )j_y the agency of the motory cells which form that mass, 

 that motion is produced in these animals. Not so in the Beroid Medusa^, where, 

 besides the action of the motory cells, the whole body, more or less spherical or 

 ovate, compact or split at one end, is kept swinnning jjy the flapping of innumer- 

 able small paddles arranged in vertical rows, like the ribs of an orange, njjon the 

 outer surface. These rows are generally eight in number, extending from one 

 pole of their spheroid body to the opposite, like the meridians of an artificial globe. 

 But, owing to the inequalities in the motions of their vertical flajipers, and their 

 radiated arrangement upon the more or less spherical body, these animals have 

 a soniewhat rotatory motion, miless the paddles move on all sides with perfect 

 steadiness and uniformity. 



There can be scarcely any thing more beautiful to behold than such a living- 

 transparent sphere sailing through the water, coursing one way or another, now 

 slowly revolving upon itself, then assuming a straight course, or retrograding, 

 advancing, or moving sideways, in all directions with equal precision and rapidity ; 

 then stopping to pause, and remaining for a time almost immovable, a slight waving 

 of some of its vibrating organs easily counterbalancing the difierence of its specific 

 gravity and that of the water in which it lives. So Pleuroljrachia may appear at 

 times, and so does it also appear when moving in a state of contraction. But 

 generally, when active, it hangs out a pair of most remarkable a^jpendages, the 

 structure and length and contractility of which are equally surjirising, and exceed 

 in wonderful adaptation all I have ever known among animal structures. Two 

 apparently simple, irregular, and unequal threads hang out from opposite sides of the 

 sphere. Presently these appendages may elongate, and equal in length the diameter 

 of the sphere, or surpass it, and increase to two, three, five, ten, and twenty times 

 the diameter of the body, and more and more ; so much so that it would seem 

 as if these threads had the 250"\ver 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, forming 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 Avhole body, and Ijends in the most graceful curves. 

 These two long streamers, stretching out in straioht or imdulatiui^ lines, sometimes 



