TUNIC ATA. 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 Appendicular iidcR, and four 

 genera, and is represented in all seas. 



Oikopleura 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. 



