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.