I wish I had space here to give a fuller abstract
of Mr. Agassiz's interesting observations on the development of the
pedicellariae. All possible gradations, as he adds, may likewise be found
between the pedicellariae of the star-fishes and the hooks of the
Ophiurians, another group of the Echinodermata; and again between the
pedicellariae of sea-urchins and the anchors of the Holothuriae, also
belonging to the same great class.
Certain compound animals, or zoophytes, as they have been termed, namely
the Polyzoa, are provided with curious organs called avicularia. These
differ much in structure in the different species. In their most perfect
condition they curiously resemble the head and beak of a vulture in
miniature, seated on a neck and capable of movement, as is likewise the
lower jaw or mandible. In one species observed by me, all the avicularia
on the same branch often moved simultaneously backwards and forwards, with
the lower jaw widely open, through an angle of about 90 degrees, in 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.
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