570 HISTORY OF SYSTEMS. 



between the stars were filled with eggs of different sizes, " each adhering by 

 one end to a very fine capillary filament. The smallest eggs are globular, 

 and as they advance in size, they change to an oval figure ; whence they 

 assume the shape of one of the radii of the stars." Ellis ascertained " that 

 each radius is a distinct animal by itself." Lib. cit. x. 671. — In his Essay 

 on Corallines, Ellis described another species, but his account of its structure 

 is very inaccurate. 



Pallas and Linnaeus referred these species to the genus Alcyonium, under 

 a false view, evidently, of their organisation. Gaertner confirmed Ellis's 

 opinion that each ray of the star was a separate animal ; and, after a long- 

 interval, MM. Peron and Lesueur and M. Desmarest described one or more 

 other species, indicating their structure to be of higher complexity than other 

 polypes, without, however, attempting to give them a proper position or 

 arrangement in the Animal Kingdom. For this great step in classification 

 we are entirely indebted to M. Savigny, who published his " Memoires sur 

 les Animaux sans Vertebres" in 181(5. 



His systematic table of the Tunicata is as follows : — 

 Animaux invertebres non articules. 

 Mollusques hermaphrodites et acephales. 



Class— ASCIDIJE. 



Shell soft, formed by an exterior distinctly organised envelope, furnished 

 with two apertures, a branchial and an anal one. Cloak forming an interior 

 tunic, also furnished with two apertures corresponding with those of the 

 shell and adherent to them. Branchia occupying wholly or in part the sur- 

 face of a membranous cavity attached to the inner surface of the cloak. 

 Mouth without labial laminae, and situated at the bottom of the respiratory 

 cavity between the two branchiae. 



Order I. Ascidi^e Tethydes. 



Cloak adhering to the envelope or shell only by the two apertures. 

 Branchia equal, large, forming the two side-walls of the respiratory cavity. 

 Branchial orifice furnished interiorly with a membranous and denticulated 

 ring, or with a circle of filaments. 



1. Family — TethyjE. 

 Body fixed. Apertures not opposite nor communicating by the cavity ol 

 the branchiae. Branchial cavity open at the superior extremity only, and its 

 aperture furnished with tentacular filaments. Branchia; united or coalescent 

 on one side. 



I. Simple Tetiiyes. 



1. Section. Apertures with four rays. 



1. Boltenia. Body pedunculated. 



2. Cynthia. Body sessile. 



2. Section. Apertures tvith more than four rays, or ivithout distinct rays. 



3. Phallusia. Body sessile. 



4. Clavelina. Body pedunculated. 



II. Compound Tethyes. 



3. Section. Both apertures with six regular rays. 



5. Diazona. Body sessile, orbicular ; a single svstem. 



6. Distoma. Body sessile, multiform ; systems several, 



7. Sigillina. Body pedunculated, conical, vertical ; a 



single system. 



