LOCOMOTION IN SURIRELLA. 1 53 



the ribs. Just what space may here be occupied by the sap it 

 would be difficult to determine, though I would record that 

 granules observed here had a perceptible size. No reason 

 appears, from the structure of the keel-canal, why the whole 

 strand should not be bathed in a fluid, except only the 

 actual thin film which may be supposed to fill the exceedingly 

 narrow keel-cleft to repletion, and seal it against any leakage 

 into the surrounding water. Here comes into play, no doubt, 

 the centrifugal pressure of the diatom — a pressure indicated 

 to be very great by some perfectly legitimate experiments and 

 calculations of O. Miiller. 



As concerns demonstration of obscure points in diatom 

 structure with stains, I have already had some little experi- 

 ence, and would especially mention again that a mixture of 

 Bismarck brown and tannic acid had years ago been useful in 

 making visible the coleoderm on FAinotia and distinguishing 

 it from immediately adjacent protoplasm. This stain was 

 applied to the living diatom. At the same time, sundry 

 examples of Siirirella underwent the same treatment, and I 

 was altogether unable to see in them any indication of a 

 brown-staining jelly within the keel. On the other hand, 

 eosin subsequently applied gave good stainings of the general 

 protoplasmic mass of Surirella, but failed to develop anything 

 of import as to the connection between it and the keel- 

 contents. There was indeed much shrinking of the rib-canal 

 protoplasm, extending often to a complete retirement into the 

 body of the frustule. * It was evident enough that for 

 Surirella previous fixing of the protoplasm was a requirement 

 for successful staining. So now, having a desire to develop 

 into unquestionable visibility the keel-contents, I made only 

 small experiments — which led to very little — with stains 

 applied in this manner, but proceeded to fix the diatoms in 



^ *L,auterborn speaks of Uiionin ami methyl violet, and mentions that 

 his preparations showeil the contracteil strand " in the keel torn loose 

 from the plasma." 



