THE TUNICATA. 



515 



tures are at opposite ends of the longest diameter of the 

 body ; and, in the two latter, locomotion is effected by the 

 contraction of transverse muscular bands, which drives the 



Fig. Ii8.—Phal!u3ia mentida.— The test is remove'1. and liarrlly more of the animal 

 represented than would he seen in a lon.iitiidinal section: a. oral aperture; b, 

 gaii.2;lion; c, circlet of tentacles ; d, branciiialsac— the three rows of aoertures in 

 its lipper part indicate, but do not represent, the stifjmata; e. the laniruets ; /, the 

 oesophasreal openin«: ; g, the stomach ; h, the intestine; ?, tne anus ; k\ the atrium; 

 I, the atrial aperture ; m, the endostyle ; w, the heart. 



water otit of the one aperture or the otlier, and causes the 

 body to be propelled in the opposite direction. 



When one of the simple fixed Ascidians, such as a Phal- 

 lusia (Fig. 148) or a CyntJiia, is laid open by a section car- 



