CLASS VI. ANNELIDA: ORDEE 2. TUBICOLA. 617 
THE LEODICB ANTBNNATA. TEEEBELLA MEDUSA IN ITS CASE. OUT OF ITS CASE, 
a smooth covering of hardened mucus ; in others, it is of a leathery or horny consistency ; and 
in some it is composed, Hke the shells of the mollusca, of calcareous matter secreted by the 
animal. The annexed engravings show one species, the Terehella Medusa, with incrustations and 
also without, that is, in its natural state. 
All these worms are unisexual. They deposit their eggs in a mass of mucus, which usually 
clings to the tube of the parent animal. 
The Serpulm, which form irregularly twisted calcareous tubes, often grow together in large 
masses, generally attached to shells and similar objects; while those genera which, like the 
Terehella, build their residences of sand and stones, appear to prefer a life of single blessedness 
Vol,. II.— V8 
