148 THE HARMONIES OF NATURE. 



in form from the associated ones. Yet, strange to say, these 

 solitary salpao are the young of salpse that have been chained, 

 and the progeny of these solitary ones will be chained salpse ; 

 consequently, as Chamisso, the first discoverer of this remark- 

 able alternation of generations, graphically observes, 'a salpa 

 mother is never like its daughter or its own mother, but 

 resembles its sister, its grand-daughter, and its grandmother.' 



The tubular body of the salpae is open at both ends, the pos- 

 terior aperture being provided with a more or less perfect val- 

 vular apparatus, which can be opened or closed at pleasure. 

 They move slowly along by alternate expansions and contractions, 

 by admitting the water through the posterior aperture, and ex- 

 pelling it through the opposite orifice. 



The Pyrosomes consist, like the compound Ascidians, of large 

 colonies of small individuals aggregated in the form of a cylin- 

 der open at one end. Their mouths or anterior extremities are 

 situated on the exterior of this hollow body, which they bristle 

 with large and longish tubercles, whilst the opposite or anal 

 orifices open into the cavity of the cylinder, whose smooth wall 

 they perforate with numerous small holes. By a simultaneous 

 action the central cavity is either narrowed or enlarged, and by 

 this means the strange social republic glides slowly through the 

 waters. They inhabit the Mediterranean, and the warmer 

 parts of the ocean. In the former, at times, their abundance is 

 a source of dread to the fishermen, sometimes even completely 

 clogging their nets ; and in certain oceanic regions they are met 

 with in almost incredible profusion. Their delicate and trans- 

 parent forms, their elegant tints, and their unrivalled phosphor- 

 escence render them the most beautiful of molluscs, and objects 

 of admiration to the naturalist and the voyager. 



Mr. Bennett relates that, during a voyage to India, the ship, 

 proceeding at a rapid rate, continued during an entire night to 

 pass through distinct but extensive fields of these molluscs, 

 floating, and glowing as they floated, on all sides of her course. 

 Enveloped in a flame of bright phosphorescent light, and 

 gleaming with a greenish lustre, the pyrosomes, seen at night 

 in vast shoals upwards of a mile in breadth, and stretching out 

 until lost in the distance, present a spectacle the glory of which 

 may be easily imagined. 



( In the evening of the 13th Frimaire,' says M. Peron, who 



