534? Natural History of Molluscous Animals. 



water muscles, of the accuracy of which I am, however, by 

 no means satisfied.* The scallops (Pecten), it has been 

 asserted, can even leap by first opening their valves to the 

 utmost, and then closing them by a strong and sudden effort. 

 When deserted by the tide on any occasion, they will tumble 

 forward in this way until they have regained the water. Nay, 

 some popular writers repeat a story from the ancients that 

 these scallops can rise up from their beds in the deep, and 

 navigate the surface, having one valve raised and exposed 

 with its concavity to the breeze, while the other remains 

 under the water, and answers the purpose of an anchor, by 

 steadying the animal, and preventing its being overset ; but 

 this part of their history you may safely reject. 



There is lastly an order of rather doubtful Mollusca which 

 have no shell, but merely a coriaceous membrane for their 

 envelope, and which, in consequence, have been named Mol- 

 lusca tunicata by modern naturalists. By far the greater 

 proportion of these are fixed animals, but some of them swim 

 in and on the ocean ; not, however, by the aid of any particu- 

 lar organ, but by partial contractions of their cloak. The 

 jSalpae are examples of this tribe, of which a number of indi- 

 viduals belonging to the same species will cohere together by 

 minute suckers which garnish their sides, and form floating 

 chains, more obvious, it may be, in the night season than dur- 

 ing the day, from the phosphorescent light they diffuse. The 

 Pyros6mse (Jig, 132.) are a still more singular family of the 



same order. Each seeming individual of this genus is, in fact, 

 a numerous colony of little Mollusca, each in its own cell, dis- 

 tinct, yet inseparably connected with its fellows. Collected into 

 the figure of a gelatinous cylinder, open at one extremity and 

 closed at the other, and roughened externally by a multitude 

 of tubercles disposed sometimes in rings and sometimes irre- 

 gularly, they float in the Australian seas like stars of this 

 lower world, shedding around them a halo of light, brilliant 

 indeed, but surpassed in beauty by those other colours of the 



* Smellie's Phil, of Nat. History, i. 137. 



