588 Algae. 



Tetraplacatae elles-memes ne sont qu'un stade de division des 

 Diplacatae devenu permanent. II s'en suit qu'il a du exister 

 ou, peut-etre, qu'il existe encore une forme des Tetraplacatae 

 oü les plaques se divisent transversalement et qui a donne 

 l'origine aux Okede'nie'es. 



„Chez ces dernieres la division doit certainement avoir 

 lieu dans une direction longitudinale, car la forme de leurs 

 chromatophores est ordinairement celle d'un H. Or, les tissus 

 longitudinaux de pareilles plaques representent toujours un com- 

 mencement de division longitudinale; c'est un stade de division 

 devenu permanent. C'est ainsi que la division transversale des 

 ancetres des Okede'nie'es redevient longitudinale chez ces 

 dernieres." 



L'auteur compare cette division avec le plan de division 

 du point d'accroissement de certaines algues (Sphacelaria, 

 Chaetopteris). „Seulement ce qui chez ces algues se fait dans 

 une serie de generations de cellules continue et ininterrompue, 

 s'etend chez les Diatome'es dans un espace de temps immense, 

 chaque changement n'apparaissant que dans un nouveau groupe 

 d'organismes. La raison de cette alternance pourrait neanmoins 

 etre la meme dans les deux cas." w. Arnoldi (Charkow). 



Ostenfeld, C. H. et Ove Paulsen, Planktonpröver fra 

 Nord-Atlanterhavet [c. 58°— 60° N. Br.] samlede: 1899 

 af D r. K. J. V. Steenstrup. (Plankton-samples collected 

 in the North Atlantic Ocean (Latitude 58°— 60° N.] in 1899, 

 by Dr. K. j. V. Steenstrup.) Kjerbenhavn, Medd. om Grön- 

 land. XXVI. 1904. p. 143—210.) 



The samples examined by the authors were collected by Dr. Steen- 

 strup on a voyage to Greenland in 1899 by a method invented by 

 himself. He has described the method as iollows: The apparatus used 

 for collecting consists of a brass tube, 30 cm. long, with an opening at 

 its anterior end, about 1 cm. in diameter; the bottom consists oi a piece 

 oi silk gauze, fastened down by a ring which can be screwed on ; the 

 tube is cylindrical, and has a diameter oi 4 cm. In order to keep the 

 Plankton quiet so that it may settle down at the bottom, a brass plate 

 with holes, about 3 mm. wide and placed in a circle, is fitted in front 

 of the gauze, and about 1 mm. from it. The apparatus is thus very 

 easy to manage and it can' be dragged aiter the ship like a log. — In 

 order to obtain a complete outline of the Plankton of the North 

 Atlantic Ocean at the time when the voyage was made the appara- 

 tus was continually dragged after the ship except the few minutes when 

 it was taken up to have the silk gauze changed, which was generali)- 

 done every fourth hour. Thus every Plankton-sample does not represent 

 the Plankton of one particular spot, but consists of thät taken in the 

 stretch of water between the place where the preceding one was taken 

 and the point in question. The silk gauze with the plankton collected 

 in it was put into a glass containing spirits. Of such samples 107 were 

 collected on the voyage out, and 69 on the homeward route; they all 

 contain almost exclusively microplankton, as the apparatus hardly ever 

 catches larger organisms. The result arrived at through the investi- 

 gations of the samples is shown in Plankton-tables in which is recorded : 

 1. The number of the samples; 2. the habitat; 3. the temperature of the 

 water; 4. its salinity ; 5. its colour (Forel's scale) ; 6. the times of 



