318 N. E. BROWN ON THE STRUCTURE OF DIATOMS. 



direction, and finally one piece was passed from one side completely 

 round one end to the other side, where, upon meeting the other 

 piece of dirt which was moved towards it, the invisible hands 

 moving the dirt lifted it up and placed it upon the other piece of 

 dirt and held it there, both together being then moved up and 

 down as before. Now this and other movements I have witnessed 

 could only have been made at the will of the diatom, and in my 

 opinion must have been controlled by living matter extruded from 

 the interior of the shell, and therefore there must be openings 

 through which the interior is in communication with the exterior 

 other than at the raphe, where, as is well known, a crest of proto- 

 plasm extrudes, which, from measurements I have made, varies 

 from l/14,000th to l/3,000th inch in depth and l/6,000th to 

 1/1. 800th inch in breadth. Feeling convinced of this, I sought 

 for several years for evidence of pores in Pinnularia without 

 finding the slightest trace of them, and all authors I have con- 

 sulted state that there are no openings in the valve of Pinnularia 

 other than at the raphe. With respect to diatoms in general,, 

 in the 8th edition of The Microscope and its Revelations (1901), 

 p. 590, it is stated, " We have in fact no positive demonstration 

 of the existence of special apertures communicating between the 

 outside and inside of the cell." 



However, some four years ago I obtained a sample of the 

 Chei-ryfield diatomaceous deposit, and upon mounting some of it 

 in picric piperine, found that it contained four or five species of 

 Pinnularia, on one of which I at last saw indications of the pores. 

 I had so long sought. This species is one of the smallest in the 

 material and the only one on which I have been able to see any 

 indication of pores. They are only to be seen when the outer 

 surface of the cavities is accurately in focus and the light central, 

 and are so minute and crowded that they appear like a single 

 dusky beaded line extending all the way along the centre of the 

 cavity, and they do not appear to be present at any other part. At 

 any focal plane below the external surface, such as when the large 

 opening into the interior of the diatom is in view, they cannot be 

 seen. When viewed from the inside of the valve they are scarcely 

 visible except where seen through the large opening of the cavity 

 into the interior. Although a distinct bead-like appearance is just 

 discernible, the pores are so closely placed that neither I nor the- 

 friends to whom I have shown them, have been able to see them 



