DIATOMACEJfc. 425 



in the side view they appear attached to the right and left 

 edges of the interior of the frustule. This colourless 

 granular substance carries in its centre, near the middle 

 part of the Diatom, an imperfectly developed nucleus 

 which it is not very easy to see, but may be easily de- 

 monstrated by the application of acid. The colourless 

 substance is what, in other Diatoms, Schultze shows to be 

 Protoplasm, or vegetable sarcode, and which contains 

 numerous small refractive particles. On adding a drop of 

 hyperosmic acid, these are coloured blue-black, and prove 

 to be fat. It is, however, exceedingly difficult to deter- 

 mine the exact limitations of the protoplasm, on ac- 

 count of the highly refractive character of the siliceous 

 shell, and the obstruction presented by the bands of 

 endochrome. 



After a short distance, the protoplasm reappears, and 

 is contracted into a considerable mass within the conical 

 terminations of the frustule. Schultze observed in this 

 part of the protoplasm a rapid molecular movement such 

 as is known to occur in the Closterium, and further, a 

 current of the granules of the protoplasm along the raphe. 

 Pleurosigma angulatum " crawls" as do all Diatoms pos- 

 sessing a raphe, along this line of suture. To crawl along, 

 it must have a fixed support. He believes free swimming 

 movements are never to be observed in this or in any 

 other Diatom. Accordingly, Schultze invariably found 

 that the raphe is in contact with either the glass slip or 

 the glass cover, between which the Diatom is placed, or is 

 in apposition with some foreign body of considerable size. 

 Schultze repeated the experiments of Siebold, and ob- 

 served, as he and also Wenham had done long before, 

 that particles of foreign matter stick to the raphe as 

 though it were covered with some glutinous material, 

 and are carried slowly along by the action of a current. 

 This he observed in many Diatomacese, and found in- 

 variably that foreign particles adhered only to the raphe, 

 or what corresponded to it. "There is obviously," says 

 Schultze, " but one explanation ; it is clear that there must 

 be a band of protoplasm lying along the raphe, which 

 causes- the particles of colouring matter to adhere, and 

 gives rise to a gliding movement. For there is but one phe- 



