125 



On Diatom Structure. 



By T. F. Smith. 



(Read June 24th, 1887 J 



It is not my intention to-night to read an exhaustive paper 

 on diatom structure; to do so would be to attempt to thresh 

 out an already well-threshed-out subject, and an insult to the 

 intelligence of the members of this Club ; several of whom 

 certainly, and the whole probably, know more about the subject 

 than myself. There are, however, still a few outstanding 

 matters in connection with the structure of the more complex 

 diatoms ; such as the position, and the absence or presence of 

 certain membranes that still remain in abeyance ; and, possess- 

 ing several slides, as I do, that seem to me to carry the ques- 

 tion a step or two further, I thought it might be of interest to 

 exhibit them here to-night, and give you my own ideas of the 

 structure shown. 



It would be useless, however, to try to get at the finer struc- 

 ture of diatoms with dry or even water-immersion lenses ; for 

 however good in themselves, the limit of angle is reached, and 

 you can get no further ; but Messrs. Swift and Son have 

 kindly furnished me with four stands and glasses, in addition 

 to my own, and I am consequently enabled to show you five 

 of my objects at once, under jV' oil-immersion lenses. Should 

 you, however, find any deficiency in the manner in which they 

 are shown, I must ask for your forbearance, as I am new to 

 the work, and this is the first time I have attempted to exhibit 

 anything in public, and unfortunately, at a time like this, the 

 demonstrator is more likely to exhibit himself than the objects. 



On May 28th of last year you were fortunate enough to have 

 two papers on diatom structure read before you in one night ; 

 one by Mr. Morland, and the other by Mr. Deby ; and, with 

 the exception of the discrepancy between them of a closed 

 membrane, or the want of one, those papers may be said to 

 embody the ideas of general structure brought up to date. 



