ASCIDIA. 



445 



produced varies markedly in the different forms. In some 

 forms the " test "-cells make calcareous spicules. 



In. ap. 



T, 



En. 



FIG. 240. Dissection of Ascidian. After Herdman. 



In. a/>., Inhalant aperture ; T., test, cut away below to show mus- 

 cular layer, pharynx, etc. ; En., endostyle or ventral groove 

 of pharynx. Note removal of pharynx to show, on the other 

 the left side, stomach (St.), intestine (with fold seen at inci- 

 sion), and reproductive organs (G.); //., opening of pharynx 

 into oesophagus; G.D., genital duct; A., anus; C7., cloacal 

 chamber; Ex. ap., exhalant aperture; Gn., lies above the 

 ganglion, which is seen between the two apertures ; beneath it 

 is the sub-neural gland and its duct. 



Body wall and muscular system. The body wall, mantle, 

 or tunic, disclosed by peeling off the test, is a structure of 

 considerable complexity. Its outer surface is covered by a 



