588 TITNICATA. 



and their discoveries have been since extended by the 

 laborious researches of Sars and Loven. 



It was among these singular beings that Van Has- 

 selt discovered " a heart of such extraordinary charac- 

 ter, changing incessantly its auricle to ventricle, and its 

 ventricle to auricle, its arteries to veins, and its veins to 

 arteries." Among the Salpian Tunicaries it was, moreover, 

 that Chamisso made the no less extraordinary discovery 

 that " a Salpa-mothev is not like its daughter or its own 

 mother, but resembles its sister, its granddaughter, and its 

 grandmother." The Pyrosomes afford a spectacle to the 

 naturalist of unexampled beauty when, seen by myriads 

 from the vessel in the night, they gleam with phosphor- 

 escent radiance, forming vast shoals of mimic pillars of fire, 

 illuminating all around with a green unearthly glare. The 

 most curious feature, however, in the history of these soft- 

 shelled Mollusks is the fact that many among them 

 form communities of beings like the Corals, " a com- 

 monwealth of beings bound together by common and vital 

 ties. Each star is a family, each group of stars a commu- 

 nity. Individuals are linked together in systems, systems 

 combined into masses." All the Tunicaries are free in 

 their young or larval state, but afterwards become fixed to 

 rocks, algae, shells, and other marine bodies; some, how- 

 ever, as the Salpians and Pyrosomes, remain always free, 

 floating in the water. 



The Tunicaries have certain affinities with the Bryozoa, 

 but their closest relationship seems to be with the other 

 Acephalous Mollusca with calcareous shells. "Were the 

 test of an Ascidian," says Professor E. Forbes, " converted 

 into a hard shell, symmetrically divided into two plates, 

 connected together dorsally by cartilage, and capable of 



