ANNOTATIONS AND ADDITIONS. 55 



living organic beings, is principally due, in the class of Zoo- 

 phytes, to the Acalephae (the families of Medusa and Cyanea), 

 to some Mollusca, and to a countless host of Infusoria. 

 Among the small Acalephse, the Mammaria scintillans offers 

 the beautiful spectacle of, as it were, the starry firmament 

 reflected by the surface of the sea. This little creature, when 

 full grown, hardly equals in size the head of a pin. Michaelis, 

 at Kiel, was the first to show that there are luminous sili- 

 ceous-shelled infusoria : he observed the flashing light of the 

 Peridinium (a ciliated animalcule), of the cuirassed Monad 

 the Prorocentrum micans, and of a rotifera to which he gave 

 the name of Synchata baltica. (Michaelis iiber das Leuch- 

 ten der Ostsee bei Kiel, 1830, S. 17.) The same Synchata 

 baltica was subsequently discovered by Eocke in the Lagunes 

 of Venice. My distinguished friend and Siberian travelling 

 companion, Ehrenberg, has succeeded in keeping luminous 

 infusoria from the Baltic alive for almost two months in 

 Berlin. He shewed them to me in 1832 with a microscope 

 in a drop of sea-water: placed in the dark I saw their 

 flashes of light. The largest of these little infusoria were 

 l-8th, and the smallest from l-48th to l-96th of a Paris 

 line in length {a Paris line is about nine-hundredths of an 

 English inch) : after they were exhausted, and had ceased to 

 send forth sparkles of light, the flashing was renewed on 

 their being stimulated by the addition of acids or of a little 

 alcohol to the sea-water. 



By repeatedly filtering water taken up fresh from the sea, 

 Ehrenberg succeeded in obtaining a fluid in which a greater 

 number of these luminous creatures were concentrated. 



