SEA SQUIRTS. 



239 



animal nature : it is composed of soft though powerful muscu- 

 lar tissue, and by its contraction the water, which always fills 

 the interior of this " leather bottle," can be violently spurted 

 forth a phenomenon which has brought upon these creatures 

 the name of Sea-squirts. This muscular coat is known as the 

 mantle. 



The Ascidian has no proper system of blood-vessels, as we 

 are generally acquainted with them in higher animals. The 



ORANGE-SPOTTED SQUIRT (Cynthia aggregata). 



blood flows about the general body cavity, and is not confined 

 to narrow channels as in our arteries and veins. There is a 

 heart, it is true, but one of the simplest character, without any 



9 



