4 THE STRUCTURE AND LIFE 



Mr. Otto Miiller, of Berlin, who has attempted to elucidate some of 

 the most difficult points in the anatomy and physiology of diatoms, has 

 published a very interesting note ( x ) on the chromatophores of Pleuro- 

 sigma angulation and Balticum, and also on those of Niizschia Sigma. 



In Pleurosigma angulation the chromatophores consist of two com- 

 paratively narrow bands, at least twice the longitudinal diameter of the 



cell. 



These bands are lobed and jagged but not perforated; they are placed 

 symmetrically on each side of the cell and are applied to the cellular 

 wall, from which they are only separated by a thin bed of protoplasm. 

 The median portion of each chromatophore is undivided, and is applied 

 to the superior valve (a name given by Otto Miiller to the valve which 

 contains the median portion of the chromatophore). Two pieces (together 

 equal to the median portion) are placed separately on the inferior valve 

 while the ends of the chromatophore which penetrate into the extremi- 

 ties of the valve are turned towards the connecting parts and there join 

 the pieces proceeding from the superior and inferior valves. 



The active part of the chromatophore is thus spread almost equally 

 on each side of the surface of the protoplasm of the cell. 



The median line of the chromatophores coincides, in the same way 

 as in Navicula, with those ot the connecting parts ; but the parts 

 which are thrown back on the valves are not placed symmetrically in 

 relation to the plane of division. In the centre of the median part of 

 each chromatophore, which is placed on the superior valve, on either 

 side of the raphe there is a rounded opening giving rise to a nearly 

 circular blank space round the raphe. 



Pleurosigma Balticum also contains chromatophores, the median line 

 of which coincides with that of the connecting parts and which spreads 

 itself on both sides over the valves. These chromatophores are not 

 long-folded bands, as in Pleurosigma angulation, but are very jagged and 

 perforated plates. 



PL Hippocampus Sm. has similar plates to the last. 



Otto Miiller has in a similar manner investigated Nitzschia Sigma. 

 In this species there is only a single chromatophore which is completely 

 divided by the nucleus. This chromatophore is in the form of a plate, 

 and is applied to the connecting part opposite the two keels. 



( ' ) Otto Miiller : Die Chromatophoren mariner Bacillariaceen aus den Gattungen Pleuro- 

 sigma und Nitzschia. Vorlaufige Mittheilung ; Nov., 1883, in Berichte der Deutschen 

 Botanischen Gesellschaft (1883) i. pp. 478-84; J.R.M.S. 1884, p. 274. 



