a most remarkable and interesting community of minute animals, a polymorphic hydroid colony, well worth most exhaustive investigation. Several species and genera of hydroids are found upon the shells of hermit-crabs, but they are usually pretty much alike in general organization; and our Fig. 1, which is a highly magnified drawing of a small portion of a colony of the hydroid larvæ of Dysmorphosa, will serve to represent their character.
The crust on the surface of the shell consists of a network of tubes, cemented to the shell and to each other in a mass from
Fig. 1.
which the bodies of the individual hydras protrude, somewhat as the stem of a tree rises erect from the creeping root, although the community is more like a thicket of suckers than a single tree, for all its members spring from one system of roots, and, although
