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TUNICATA. 
The Tunicata are marine animals, the majority of which live, in 
their adult stage, a stationary life, fixed to the rocks or sea-bottom, 
but a comparatively small number are free-swimming. 
They occur in the form of cartilaginous or leathery sacs, fleshy in- 
crustations, solid fleshy masses, free-swimming, barrel-shaped animals, 
solitary or united into chains or hollow cylinders ; or, lastly, of minute 
Fig. 1. 
Wall Case 
to left 
of main 
entrance 
to Shell 
Gallery. 
Ascidia mentula from the right side. 
at, atrial aperture ; br, branchial aperture ; t, test. 
[After Herdman : Tunicata, Encyc. Britannica.] 
free-swimming tadpole-shaped organisms. To explain briefly the 
structure of a Tunicate, Ascidia mentula (Fig. 1), is selected. The 
G 2 
