" The avicularia, like the vibracula, probably serve for defence, but they also catch and kill small living animals, which, it is believed, are afterwards swept by the currents within reach of the tentacula of the zooids.

Some species are provided with avicularia and vibracula, some with avicularia alone and a few with vibracula alone.

It is not easy to imagine two objects more widely different in appearance than a bristle or vibraculum, and an avicularium like the head of a bird; yet they are almost certainly homologous and have been developed from the same common source, namely a zooid with its cell.

Hence, we can understand how it is that these organs graduate in some cases, as I am informed by Mr.

Busk, into each other.