458 NOTES AND MEMOBANDA. 



the genus of cousidcrablo importance from a systematic point of view, 

 as exhibiting a clear affinity with the lower forms of the Schizomy- 

 cetes, especially the Bacteria. 



Halosphaera, a new Genus of Unicellular Algae (Plate XVI.). — 

 Dr. F. Schmitz gives an extremely interesting description of a new 

 form of unicellular marine algje, under the name Halosphcera viridis* 



It presents the appearance of minute green points just visible to 

 the naked eye, the largest being a little more than half a millimetre 

 in diameter, floating on the surface of the water in the Bay of Naples, 

 and long known under the designation "punti verdi." It is to be 

 found regularly in the spring from the middle of January to the 

 middle of April, when it disappears. The light green globule, which 

 has no independent power of motion, is enclosed in a tolerably thick, 

 smooth, and perfectly colourless membrane ; the inside of this mem- 

 brane is clothed with a thin layer of protoplasm, enclosing a single 

 very large central vacuole with colourless cell-saj). Imbedded in the 

 protoplasmic layer are a small number of minute chloroi)hyll-grains, 

 and a single globular nucleus with a somewhat darker nucleolus. 



The process of cell-division which takes place during the develop- 

 ment of this alga is very interesting, and altogether in accordance, in all 

 essential points, with that described by Strasburger in his ' Zellbild- 

 unf und Zelltheilung' as occurring in the tissue of more highly 

 organized plants. As the cell increases in size, the nucleus divides 

 into two, which gradually separate from one another, and again undergo 

 division (Fig. 1) ; and, as this process is rej)eated many times, a very 

 large number of nuclei, from 200 to 300, come to be tolerably regularly 

 dispersed throughout the protoplasm of the mother-cell. The mother- 

 cell has now attained its full size, and the division of its contents into 

 daughter-cells commences, the protoplasmic layer gradually collecting 

 around the nuclei, so that each becomes the centre of a new jirimordial 

 cell (Fig. 2). This process takes place slowly, so that its various stages 

 can be closely followed. The space between the daughter- cells appears 

 to be occupied only by a colourless cell-fluid ; the cells having the 

 form of hemispherical balls in close contact with the inner mem- 

 brane. They are of a bright green colour, but no seixarate chlorophyll- 

 grains are to be detected in them. These become the mother-cells of 

 the zoospores. The outer membrane of the entire cell has in the 

 meantime become differentiated into two distinct layers, of which the 

 outer one now bursts by a nearly circular slit, and slips off the inner 

 membrane, which now itself clearly consists of two layers. This 

 layer next begins to swell up and deliquesce, and at length becomes 

 resolved into mucilage. As soon as this change commences, the hemi- 

 spherical green daughter-cells begin gradually to detach themselves 

 from the outer membrane, and to distribute themselves over the 

 interior of the cell (Figs. 3, 4, 6). Each of them usually divides into 

 two zoospores, though sometimes a larger number, and sometimes only 

 one, are developed from each daughter-cell (Figs. 7-15). In the 

 ordinary case the green primordial cell first of all contracts in the 



* 'Mittiieil. Zool. Station Neapcl,' i. (1878) G7. 



