228 THE AMERICAN MONTHLY [Aug. 



as large as the end of the sliding block, is cut out, at the 

 point where it crosses the slot, and a piece of metal is 

 tacked over it below, making a recess in which the block 

 is held when the set-screw is put in place. 



The observer should be seated upon a chair the height 

 of the stand when closed. The projecting ends of the 

 lamp-carrier form handles by which the inner box may 

 be lifted. The lamp and its attachments should be re- 

 moved from the carrier when not in use. 



Although primarily designed for the use of the micro- 

 scope in an erect position, the stand has proved equally 

 satisfactory with the instrument inclined. Indeed, for 

 prolonged use by artificial light, it would be diflicult to 

 find a support by means of which so much of the wear 

 upon the observer is done away with. 



As the stand is not patented, anyone is at liberty to 

 have it made, and it is the sincere wish of the writer 

 that all who do so may find pleasure and profit in its use. 



The Diatom Considered as a Protozoan, with Method of 

 • Demonstration. 



By K. M. CUNNINGHAM, 



MOBILE, ALA. 



The article which appeared in the last issue of this 

 periodical, entitled, " Studies in the Biology of the 

 Diatoms," dealt more particularly with the motion, and 

 epidermal covering of the diatom as presented by a 

 number of species belonging to various genera. It has 

 prepared the way for a further elucidation and study of 

 the cause of their travelling movements, hitherto mys- 

 terious and puzzling. 



Immediately on closing that paper, I resumed my 

 verification studies of the various phenomena recorded in 

 " A contribution to the Life history of the Diatomaceae, 

 by Prof. H. L.Smith," as referred in my preceding paper. 



