Marine Plankton from the East-Greenland Sea. 



275 



new, as we have the excellent description and drawings of this 

 processus in Chæt. decipiens by Gran (1904). I have only to refer 

 the reader to this paper and to Gran's paper of 1902 (Rep. Norweg. 

 Mar. Fish. Investig., vol.2, No. 5) in which the microspore formation 

 in Rhizosolenia styliformis was described and where considerations 

 on the microspore problem in general were put down. Similar con- 

 siderations embrazing all the known cases of microspore formation^ 

 are given by G. Karsten (Valdivia-Exp., Phytoplankton d. Atlant. 

 Meeres, 1908). 



The annexed figures (Fig. 9) show the different stages in the 

 development of the micro- 

 spores; they correspond rather 

 closely to Gran's figures (1904). 

 In the left drawing we find a 

 chain the end cell of which 

 is a normal cell in rest and 

 contains but one nucleus, 

 while the two other cells 

 have fulfilled the division of 

 the nucleus into two daughter 

 nuclei. It might be supposed 

 that this stage could illustrate 

 the beginning of an ordinary 

 cell-division as well as the 

 beginning of the microspore 

 formation, but this is not right as there is a great dilTerence which 

 will be clear if we compare this drawing with the fig. 1 by Gran 

 (1904); this author gives here the corresponding stage of an ordinary 

 cell-division, and his drawing shows that contemporaneously with 

 the division of the nucleus a fissure in the plasma appears as the 

 first beginning of the future foramen between two cells. This fissure 

 does not exist in my case, whereby it is proved that we have here 

 the first stage of microspore formation. 



The other figures show stages with 2, 4, 8 and 16 daughter 

 nuclei corresponding rather well to the figures by Gran, but his 

 material has been better stained than mine. Perhaps we have herein 

 the explanation of the following difference, viz.: that the division 

 of the nuclei in my material goes on a good time before the divi- 

 sion of the plasma, thus e. g. in the figure to the right we have 16 

 nuclei, but only (7— )8 plasma-lumps each containing 2 nuclei. 

 With regard to the further fate of the microspores preserved ma- 

 terial does not allow observations, and to the theoretical con- 

 siderations set forth by Gran, Bergon and Karsten I have nothing 



21* 



Fig. 1). Chaetoceras decipiens CI. Cells in 

 microspore-formation. 250 t. m. 



