ANIMAL KINGDOM. 229 



our complete satisfaction, that each ray is a distinct ani- 

 mal, having its mouth at its external extremity and its rec- 

 tum opening into a common cavity, which is the centre of 

 the whole star. If the mouth of one of these rays be 

 touched, that animal alone contracts itself; whereas if the 

 centre of the star be irritated, every individual composing 

 the system is equally contracted. Nevertheless, the ju- 

 dicious observations of our countryman Ellis on this sub- 

 ject were long neglected, and until the second part of 

 the Memoires sur les Animaux sans Vertlbres made its 

 appearance every system of Botryllus was considered 

 as one Polype, and every Polype as one tentaculum ; 

 though anatomy now shows that each of these pretended 

 tentacula is provided with its own intestinal canal, its own 

 branchiae, viscera and ovaries. The rays of a Botryllus 

 as well as each of those innumerable little beings com- 

 posing the elegant Pyrosoma, which by its phosphores- 

 cence charms many a dreary night on the Atlantic Ocean, 

 and makes the sea to vie with the rainbow in brilliancy and 

 variety of colour, — these all lead us to the Ascidm and 

 Salpa, which though no longer compound animals, still 

 exhibit the same essential plan of construction. The 

 Ascidia clavata of Cuvier (Clavellina borealis Sav.) in 

 particular, affords us a disposition of the viscera which 

 exactly resembles that of the compound Tunicata. The 

 compound animal does not however become at once di- 

 stinctly simple, for in general the individuals of the same 

 species of Ascidia are grouped together, and when thus 

 grouped put on an appearance of ramification ; though 

 this, as Cuvier observes, is not real, nor does it establish 

 any organic union between the individuals, like that which 

 exists in a BQtryllus. The Salpa also are generally found 



