250 



TUNIC AT A. 



which we will select one of the simplest for special 

 description. 



The Ascidians (Ascidia)^ (Fig. 188) are met with 

 everywhere in abundance on the shores of tlie ocean, 

 but very generally are passed unnoticed by the 

 casual observer. In their natural condition, they 

 are found fixed to the surfaces of rocks, seaweed, or 

 other submarine bodies, and frequently glued to- 

 gether in bunches. Incapable of locomotion, and 

 deprived of any external organs of sense, few animals 

 seem more helpless and apathetic than these ap- 

 parently shapeless beings ; and the anatomist is sur- 



FlG. 189. — DIAGRAM OF STKUCTDRE OF ASCIWAN. 



* acTKos, askos, a leather haq. 



