384 EAMBLES OP A NATURALIST. [Ch. XXn. 



character — being in fact composed of a linear series of 

 tubular cells. 



No movement took place in any of these cells ; but mingled 

 occasionally mth this was another microscopic vegetable, 

 spherical in form, and bristling with minute rays like a 

 miniature Echinus — and about as large as a pin's head. 

 This proved under the microscope to be entirely different in 

 character from the confervoid just described, and was indeed 

 an Oscillatoria. It possessed also a gelatinous envelope, 

 which I never could find in the Trichodesmium, but was in 

 much smaller quantities than the latter. 



The naturalists of Captain Cook's third voyage observed 

 the substance I have described about New Guinea, and the 

 sailors called it sea saivdust. Peron saw it extending for 

 20 leagues from east to west, of a greyish colour. Darwin 

 noticed it near the Abrolhos islets, and says he met with an 

 allied, but smaller, species off Cape Leeuwin, Australia; 

 but none of the observers appear to have looked upon it as 

 an every-day phenomenon, as it certainly appeared to be in 

 the China Sea. Moreover, although it has been settled that 

 the conferva observed by these travellers in different parts 

 of the ocean is of the same species as that which discolours 

 the Eed Sea, I am myself very strongly of opinion that this 

 is an error, and that it wiH be found that several species of 

 this remarkable little Alga exist in different parts of the 

 world. The two forms I have described are both of them 

 in many respects different from Trichodesmium Ehrenbergii 

 — nor have they much in common with the second recog- 

 nised species, T. Hindsii.* 



* For a more complote account of this substance, the reader is referred to a 

 paper recently road at the Eoyal Microscopical Society, and which will he 

 found in the " Microscopical Journal" for April 1868. 



