STRUCTURE OF ASCIDIAN 



produced varies markedly in the different forms, 

 forms the " test "-cells make calcareous spicules. 



In. up. 



In some 



— En. 



Fig. 285. — Dissection of Ascidian. — After Herdniaii. 



In. ap.. Inhalant aperture ; T., test, cut away below to show mus- 

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

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

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

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

 into oesophagus; G.D., genital duct; A., anus; CI., 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 struc- 

 ture of considerable complexity. Its outer surface is 



