390 Mr. J. D. Macdonald on a new Polyzoon, 



The facts which I have just described, seem to be a copy of 

 those made known by that learned naturalist. 



In the digestive tube of the Termites, I have found a consider- 

 able number of parasites. 



XXXI. — Brief Description of a Ctenostomatous Polyzoon, allied 

 to Vesicularia, occurring on the Australian Coast. By John 

 Denis Macdonald, Esq., Assistant Surgeon R.N.* 



In one of our visits to Moreton Bay, the sean was hauled at More- 

 ton Island, and amongst the masses of sea-weed, &c. brought up 

 with the net, I found numerous specimens of a very beautiful Poly- 

 zoon, a small portion of which I had previously dredged at Port 

 Stevens from a depth of 5 or 6 fathoms. 



The polypidom may be said to have consisted mainly of rooted, 

 spreading and plant-like portions, and short, straight creeping trunks, 

 connected at both extremities with the fixed part of the former, so 

 that the whole presented the appearance of an open lace-work, having 

 all the transparency and lustre of glass. 



The trunks and branches were nearly perfectly cylindrical, and 

 composed of an outer membranous sheath distended with a clear 

 fluid (which escaped with considerable force when the sheath was 

 ruptured), and line-like reticulated vessels disposed in one plane, so 

 as to communicate laterally with the polyp-cells, and divide the axis 

 longitudinally into equal halves. The more central canals of this 

 vascular plane combined to form a compound vessel, which opened 

 into a spherical sinus with cellular parietes at the base of each branch. 



The ramification of the polypidom generally exhibited a trichoto- 

 mous arrangement, with simple articulations occurring only where the 

 branches were given off. 



The cells were clustered in linear series on opposite sides of the 

 branched axis, oval in shape, corneous in texture, with a terminal 

 combed aperture, folding inwards by the contraction of four equi- 

 distant sets of muscular fibres, which imparted a quadrilateral figure 

 to the opening. 



The polypes were very minute, but exhibited distinctly all the im- 

 portant points of structure observable in those of Vesicularia and 

 Bowerbankia, between which genera this polyzoon would appear to 

 lie. The ciliated tentacula, like those of Vesicularia, are eight in 

 number, and do not possess the motionless hair-like processes which 

 project from the back of each in Bowerhankia. 



Although too much importance must not be attached to the actual 

 number of tentacula surrounding the oral aperture, the tendency to 

 multiply those organs must not be altogether forgotten. Thus, while 

 there are but eight in Vesicularia, Bowerhankia densa and Bower- 

 hankia repens possess respectively ten and twelve. 



* From the Proceedings of the Royal Society, February 19, 1857. 



