. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 2-4 Rev. T. Ilincks on the Pohjzoan A mcularium. forms is suspended. This modification, wliicli is veiy slight in degree, secures to a corresponding extent a freer range of movement. In this remarkahle variety, tlicn, the avicuhirium of the normal M. ciliata is replaced bj a well-developed organ with vibracular function, which has made a considerable advance towards the structure of the most specialized vibracula. Placed as they are on the summit of a considerable rising, at a
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 2-4 Rev. T. Ilincks on the Pohjzoan A mcularium. forms is suspended. This modification, wliicli is veiy slight in degree, secures to a corresponding extent a freer range of movement. In this remarkahle variety, tlicn, the avicuhirium of the normal M. ciliata is replaced bj a well-developed organ with vibracular function, which has made a considerable advance towards the structure of the most specialized vibracula. Placed as they are on the summit of a considerable rising, at a short distance below the orifice, the tall setse command the whole of the oral tract; and their vigorous sweep must do much to prevent the accumulation of noxious matter within its bounds. It should be mentioned that the ordinary forms of the species also occur somewhat abundantly on shells from the Queen Charlotte Islands. Another interesting modification occurs in the same species. On a large colony, obtained by Capt. Cawne Warren, ])robably from the coast of Ceylon or from Bass's Straits, the avicularium is furnished with the spinous prolongation of the mandible, and along each side of the spine a delicate membranous expansion is developed (woodcut, fig. 4), which completely alters its appearance and fits it for a new func- tion or for the discharge of the old one in a difterent way. The avicularian jaws and the vibracular setaj are replaced in tliis variety by the jlapi)er; and these varied modifications are embraced within the life-history of a single species. We are already acquainted with the changes which occur in the radical fibres of the Polyzoa correspondent with diver- sities of habitat. When the sponge or other soft substance is the site of the colony, they develop a system of hooks, to act as grapnels; when the smootli, tough frond of the sea- weed, they elaborate adhesive disks for attacliment. It would seem that a like ready adaptability to clianges of circum-
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