88 Dr. CollingwooDj on Microscopic Alga. 



the accumulation of the Alga, which, in calm weather, pre- 

 sented the appearance of a regular, smooth, cream-coloured 

 pellicle, thrown up here and there into thick folds and rugosi- 

 ties ] and where thickest of a dirty yellow colour, but never 

 red. Such a scum would cover the sea for nearly the whole 

 day, with little interruption. But if a moderate breeze were 

 blowing, and the sea Avere raised, instead of an uniform 

 pellicle, the dust would be"arranged in long irregular parallel 

 lines, bands, or streaks, extending unbroken as far as the eye 

 could reach, and always taking the direction of the wind. 

 On one occasion we crossed a single band of this character, 

 the only one seen during the day. When the sea becomes 

 rather rough, the substance is more dispersed, and I have 

 traced the bands under such circumstances with some diffi- 

 culty. Out of four times that I crossed the China Sea, I 

 observed these appearances, more or less well marked, during 

 three passages. The fourth time Avas in winter (December), 

 and during the height of the monsoon — the wind very bois- 

 terous, and the sea very rough — so that the substance was 

 doubtless so washed and thoroughly disjjersed by the waves, 

 as to be indistinguishable amidst the turmoil and foam. 



The most northerly point at which I observed its accumu- 

 lations forming a pellicle upon the surface of the sea was at 

 the north entrance of Formosa Channel, in lat. 25i° N., and 

 the most southerly point was in Rhio Strait, on the equator. 



I have described the first specimens observed, from the 

 Indian Ocean north of the line, as presenting under a lens 

 the appearance of a sheaf (fig. a), but this peculiar arrange- 

 ment I did not elsewhere meet with. There were, in fact, 

 two modes of aggregation of the vegetable filaments com- 

 posing the Alga in question. Everywhere in the China Sea, 

 in the South Indian Ocean, and in the Atlantic, the form 

 presented was that of small cylindrical bundles, more or less 

 pointed at one end, but obliquely truncated at the other (figs. 

 B, c), having an average length of -i-th to -V^h inch. They 

 were cream-coloured and opaque, and examination with a 

 lens showed that the ends were fimbriated, owing to the 

 component fibres being loose at their extremities. A third 

 form was occasionally mingled Avith these, but in very sm.all 

 quantities. It was a minute spherical body, solid and 

 opaque, about the size of an ordinary pin's head, bristling 

 with minute rays, like a miniature echinus (fig. g). This 

 form I noticed in the North Indian Ocean, and very rarely 

 in the China Sea, but, although associated Avith the sheaf- 

 and wedge-shaped Alga, it appeared to constitute a very 



