n the course of five seconds; and their movement caused the whole
polyzoary to tremble. When the jaws are touched with a needle they seize
it so firmly that the branch can thus be shaken.

Mr. Mivart adduces this case, chiefly on account of the supposed
difficulty of organs, namely the avicularia of the Polyzoa and the
pedicellariae of the Echinodermata, which he considers as "essentially
similar," having been developed through natural selection in widely
distinct divisions of the animal kingdom. But, as far as structure is
concerned, I can see no similarity between tridactyle pedicellariae and
avicularia. The latter resembles somewhat more closely the chelae or
pincers of Crustaceans; and Mr. Mivart might have adduced with equal
appropriateness this resemblance as a special difficulty, or even their
resemblance to the head and beak of a bird. The avicularia are believed
by Mr. Busk, Dr. Smitt and Dr. Nitsche--naturalists who have carefully
studied this group--to be homologous with the zooids and their
cells which compose the zoophyte, the movable lip or lid of the cell
corresponding with the lower and movable mandible of the avicularium.
Mr. Busk, however, does not know of any gradations now existing between
a zooid and an avicularium. It is therefore impossible to conjecture by
what serviceable gradations the one could have been converted into the
other, but it by no means follows from this that such gradations have
not existed.

As the chelae of Crustaceans resemble in some degree the avicularia of
Polyzoa, both serving as pincers, it may be worth while to show that
with the former a long series of serviceable gradations still exists. In
the first and simplest stage, the terminal segment of a limb shuts down
either on the square summit of the broad penultimate segment, or against
one whole side, and is thus enabled to catch hold of an object, but the
limb still serves as an organ of locomotion. We next find one corner of
the broad penultimate segment slightly prominent, sometimes furnished
with irregular teeth, and against these the terminal segment shuts down.
By an increase in the size of this projection, with its shape, as well
as that of the terminal segment, slightly modified and improved, the
pincers are rendered more and more perfect, until we have at last
an instrument as efficient as the chelae of a lobster. And all these
gradations can be actually traced.

Besides the avicularia, the polyzoa possess curio