TUNICATA. 105 
in its large test, is the little hammer-shaped body in the centre of 
the figure ; the streaked areas bound a space in which the tail lashes 
vigorously. The animal can leave its test and secrete another in a 
few hours. 
The tail is attached to the under or ventral surface of the tiny 
little barrel-shaped body, and usually points forwards ; a skeletal rod, 
the urochord, runs along its length. The branchial sac has two 
ciliated openings or gill-clefts leading directly to the exterior, and 
not opening like the stigmata of the other orders into an atrial 
cavity. 
The order contains one family, the Appendiculariidce, and four 
genera, and is represented in all seas. 
OiJcopleura cophocerca, one of the largest forms, is about half an 
inch in length. The exhibited specimens came from St. Andrews, 
Fife. Professor Mcintosh reports that occasionally specimens of this 
species occur in immense quantities, the tow-nets being filled with 
them. 
