Page:Popular Science Monthly Volume 8.djvu/67

Rh The valve is attached on all sides to the bladder, excepting by its posterior margin, which is very thin, and rests on a collar or rim, which dips deeply into the bladder. The valve can only open inward;



there are on its surface numerous glands, which have the power of absorption, but are not known to secrete.

The whole inner surface of the bladder is covered with a serried mass of processes, consisting each of four divergent arms, whence they



are called quadrifid processes. Each arm generally contains a minute, faintly-brown particle, either rounded or elongated, which shows incessant Brownian movements.

Whenever found in stagnant water the bladders swarm with