25 



II. CLAVELINID^; 



OR, SOCIAL ASCIDIANS. 



The Compound Ascidians are not so far removed from 

 tlie Simple as to be unconnected by intermediate forms. 

 It was supposed until very lately that the curious animals 

 of this class, of which one species had been described by 

 Pallas under the name of Ascidia clavata, and another by 

 Otho Frederic Midler under that of Ascidia lepadiformis^ 

 belonged to the latter section ; but Milne-Edwards has 

 shewn that the individuals of the genus Clavelina, to which 

 Savigny referred the species first named, are not always, 

 nor, indeed, usually separated from each other, but spring, 

 as it were, from a common creeping root, and multiply by 

 gemmation in the manner of the truly compound Ascidians. 

 Some years previously, Mr. Lister, in his valuable paper on 

 "The structure and functions of tubular and cellular Polypi 

 and of Ascidias," * described and figured a remarkable 

 Ascidian which he had found at Brighton on Conferva 

 elongata, and which seemed to combine the characters of 

 simple and compound Tunicata. He described it as occur- 

 ring in groups consisting of several individuals, each having 

 its own heart, respiration, and system of nutrition, but fixed 

 on a peduncle that branches from a common creeping stem, 

 and all being connected by a circulation that extends 

 throughout. Their parts are of such transparency, that 

 their interior is easily seen. Their external shape resem- 

 bles a pouch, compressed at the sides and fixed at the hind 

 part of the base upon the peduncle. 



The affinity of this curious animal, or rather group of 

 animals, with Clavelina was demonstrated by Milne-Ed- 

 wards in the memoir already cited, wherein he elevated 



* Philosophical Transactions, 1834. 

 VOL. I. E 



