I'm going on with biology again this year-veryinteresting subject; we're studying the alimentary system at present.

Like the two-layered animals, they have no body-cavity-thatis to say, no cavity distinct from the alimentary system.

Finally, we have important appendages of the alimentary tube in the bladder and urethra, which belong to the alimentary system.

The body-cavity (coeloma) is therefore a new acquisition of the animal body, much younger than the alimentary system, and of great importance.