Z TUNIC AT A. 



composing the general mass, a nnmber of stars and flowers of curi- 

 ous and complicated design. Towards the Northern shores they are 

 sombre in their colors, but in the sunny regions of the South their 

 hues assume the brightest dyes, and vie with those of the corallines 

 and ActinicB that people the Ijed of the ocean. It was in the As- 

 cidian Tunicaries that MM. Audouin and Milne-Edwards first dis- 

 covered the metamorphoses of the Mollusca, and their discoveries 

 have been since extended by the laborious researches of Sars and 

 Loven. 



It was among these singular beings that Van Hasselt discovered 

 " a heart of such extraordinary character, 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 *Sft/p«-mother is not like its daughter or its own mother, l)ut 

 resembles its sister, its granddaughter, and its grandmother." The 

 Pyrosomes afford to the naturalist, when seen by myriads from the 

 vessel in the night, a spectacle of unexampled beauty : they gleam 

 with phosphorescent 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 

 MoUusks is the fact that many among them form communities of 

 beings like the Corals, — " a commonwealth of beings bound together 

 by common and vital ties. Each star is a family, each group of 

 stars a community. Individuals are linked together in systems, 

 systems combined into masses." All the Tunicaries are free in 

 their young or larva state, but afterwards fixed to rocks, algse, 

 shells, and other marine bodies ; some, however, 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 Mol- 

 lusca 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 separation, so as to expose the mantle along a ven- 

 tral mesial line, whilst the orifices protruded at one extremity, it 

 would present the closest similarity with many bivalve Mollusks." 

 The gills in these animals have generally the form of ridges more 

 or less complicated and seldom symmetrical, and their digestive, 

 reproductive, and circulatory organs are tolerably complicated, and 

 disposed at the base of their sac-like bodies. 



