718 
Proceedings of the Royal Society 
In 1834, J. J. Lister, F.E.S.,* published a paper entitled “Some 
Observations on the Structure and Functions of Tubular and 
Cellular Polypi and of Ascidiae,” in wbicb he gave an account of 
a small species of Ascidian, afterwards described by Wiegmannf as 
Perophora listen. 
Lister pointed out the condition in which the individuals lived, 
the fact that each possessed a complete set of organs of its own, but 
that all were connected by a common circulatory system; and 
stated that “ it increases by sprouts : the two streams of the stem 
run through the bud before its organs are developed.”! 
Clavelina remained in the Ascidiae simplices till 1842, when 
Milne-Edwards published his celebrated “ Observations sur les 
Ascidies composees des cotes de la Manche.”§ 
In this elaborate work he gives an account of several species of 
Clavelina , and proposes that that genus, along with Perophora , 
should be separated from both Simple and Compound Ascidians, and 
form an independent intermediate group, to which he gives the 
name of Ascidiae sociales. This group he defines as comprising 
ascidians which reproduce by buds as well as by eggs, and which 
live united by common radiciform prolongations, but which other- 
wise are free of all adhesion to one another. “On reserverait alors 
le nom d ’Ascidies simples pour les Ascidies qui ne se reproduisent 
point par bourgeons, et qui ne vivent pas reunies en groupes, par 
l’intermediaire d’une portion commune du tissu tegumentaire. 
Enfin, les Ascidies composees se rapprocheraient de cette division 
nouvelle par leur mode de multiplication, mais s’en distingueraient 
par l’existence d’un seul corps tegumentaire commun a tous les 
individus dont se compose chaque colonie; tandis que chez les 
premiers, chaque individu possede une tunique tegumentaire qui 
lui est propre.”|| 
Milne-Edwards’ ground for separating the Social from the Simple 
Ascidians was twofold ; first the union of the individuals by stolons, 
and secondly the power they possess of reproducing by gemmation. 
Of course these two points are really only one, as the union is 
* Phil. Trans., 1834, Pt. ii. p. 365. 
t Wiegmann’s Archiv, .2 Bd., 1835, p. 309. 
+ Loc. cit., p. 382. 
§ Mem. Inst. France, vol. xviii. p. 217. 
|| Log. cit., p. 266. 
