METAMORPHOSIS OF THE CIRRHIPEDES. 37 



Thompson. It is unquestionably one of the most im- 

 portant discoveries in modern science, and, in the " flood 

 of light" which it has thrown on the whole natural 

 arrangement of invertebrate animals, is fully equal to 

 that made by Trembley on the nature of the polype. 

 As we have had no opportunity, ourselves, of verifying 

 the facts disclosed by our author, we shall give them to 

 the reader in his own words. On the evening of 

 April 28. 1823, on the coast of Ireland, near Cork, 

 Mr. Thompson captured, in a small muslin towing-net, 

 a number of minute marine animals, among which was 

 one which he considered as a nondescript. " This was 

 a small translucent animal, -y^th of an inch long, of a 

 somewhat elliptical form, but very slightly compressed 

 laterally, and of a brownish tint. When in a state of 

 perfect repose, it resembles a very minute muscle, and 

 lies upon one of its sides at the bottom of the vessel of 

 sea water in which it is placed : at this time all the 

 members of the animal are withdrawn within the shell, 

 which appears to be composed of two valves united by 

 a hinge along the upper part of the back, and capable 

 of opening from one end to the other along the front, 

 to give occasional exit to the limbs. These limbs are 

 of two descriptions ; viz., anteriorly, a large and very 

 strong pair, provided with a cup-like sucker and hooks, 

 serving solely to attach the animal to rocks, stones, &c. ; 

 and posteriorly, a pair of natatory members, articulated 

 in such a manner as to act in concert, and to give a 

 very forcible stroke to the water, so as to cause the 

 animal, when swimming, to advance by a succession 

 of bounds, after the same manner as the water-flea 

 (Daphnia) and other Monoculi, but particularly Cyclops, 

 whose swimming feet are extremely analogous. The 

 tail, which is usually bent up under the belly, is ex- 

 tremely short, composed of two joints, and terminates in 

 four setae ; and it is employed to assist in progression, 

 and in changing the position from a state of repose. The 

 greatest peculiarity, however, in the structure of this 

 animal, is its eyes, which, although constantly shielded 

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