64 



ASCIDIANS APPENDICULARIANS 



two ventral apertures). The ventral heart is simple and tubular, 

 and periodically reverses the direction of the blood-current. 



Ascidiid"? 



MoJ guilds 



Cynthnds 



JCompoundL 

 \Ascidians 



Fig. 27. — Sketch of the cnief kinds of Tunicata found in the sea. 



This Class is divided into three Orders: — The Appendicularians, 

 the Ascidians, and the Salpians (see Fig. 27). 



Order I. Larvacea (Appendicularians). 



Free-swimming pelagic forms, in which the posterior part of 

 the body takes the form of a large locomotory appendage, the 



