393 



siderably in advance of the ovary ; the intromittent organ forms a 

 prominence in the floor of the respiratory chamber, and finally the 

 generative orifices open on the right side." 



II. " On the Sea Saw-dust of the Pacific." By JOHN DENIS 

 MACDONALD, Esq., Assistant Surgeon R.N. Commu- 

 nicated by Captain DENHAM, R.N., E.R.S. Received 

 January 13, 1857. 



(Abstract.) 



In this communication the author gives a description (illustrated 

 by figures) of the remarkable little algal so frequently met with in 

 the South Pacific, scattered over the surface of the water in broad 

 streaks and patches of a pale yellowish-brown tint, and which is 

 known under the name of " Sea Saw-dust." 



After adverting to the occurrence of a similar phenomenon in other 

 parts of the globe, and citing the account given of the Trichodesmium 

 erythrceum of the Red Sea by MM. Evernor Dupont and Montagne, 

 together with a description extracted from the ' Colombo Herald ' 

 of May 14, 1844, of what was obviously an example of a vegetable 

 scum of the same kind occurring on the sea off Ceylon, the author 

 remarks, that in the instances met with by himself he did not re- 

 cognize the foetid odour so generally and pointedly spoken of in the 

 accounts of others. He then states results of his own observation 

 as follows : 



" It was rather difficult at first to determine whether our species is 

 to be referred to the Oscillatoridae or the Confervidse. In the latter, 

 a linear series of tubular cells compose the filaments, which are thus 

 said to be jointed, but in the former, although the filaments are 

 tubular, simple and continuous without actual joints, a pseudo-jointed 

 appearance is presented by the apposition of the little masses of 

 contained colouring matter. Notwithstanding, having submitted the 

 ' sea saw-dust ' of the Pacific to microscopic examination on 

 several occasions, I was much inclined to believe that the fila- 

 ments were actually jointed ; and this view is supported by the cir- 



