602 



THE INVERTEBRATA 



Class ASCIDIACEA 



Tunicata in which the aduh is sedentary and has no tail ; a degenerate 

 nervous system; an atrium which opens dorsally; a stolon (if any) 

 of simple structure; and several gill clefts, which are nearly always 

 divided into stigmata by external longitudinal bars. 



The colonial members of this group are known as "compound 

 ascidians" and are sometimes classed together as Ascidiae compositae. 

 But they are not of one origin : some of them have stolonial budding 

 and dorsal languets and are related to such solitary forms as Ciona; 

 the others, with pallial budding and a continuous dorsal lamina in 

 place of the languets, are related to solitary forms, such as Ascidia, 

 which have no epicardium and possess a dorsal lamina. 



Ciona (Figs. 443-446). Described above. 



Fig. 451- 



Magnified. 

 M. mouth 



Fig. 452. 

 Fig. 451. Clavelina lepadiformis, nat. size. From Herdman. 



Fig. 452. Two groups of individuals of Botrylliis violaceus. 

 After Milne Edwards, cl. opening of common cloaca of the group : 

 opening. 



Ascidia. Solitary; without epicardium; with the viscera at the side 

 of the body, not in an abdomen; with dorsal lamina in place of 

 languets. British. 



Clavelina (Fig. 451). Resembles Ciona in general features but is 

 colonial, owing to stolonial budding; the zooids and their tests free 

 from one another save at their bases. 



