18971 MICROSCOPICAL JOURNAL. 41 



attracted by lightning-like tiashes of little specks with 

 spiral and vibrating movements that dart from the ends 

 and sides of the moving diatom. The illusion at lii-st 

 takes the form of an idea that the diatom is discharg- 

 ing nettle-like threads, and as quickly retracting them. 

 Should the mind get caught under this spell once, it will 

 be a material duration of time before the observer, fascin- 

 ated by this illusory appearance, can dissociate his mind 

 from the idea that what is seen is not a part of the vital 

 function of the ectoderm of the diatom, and properly re- 

 fer this action to the parasitic colonies of Spirilla, which 

 seem to be living in symbiosis with their host the Navi- 

 cula. 



How to Make and Stock a Fresh-water Aquarium. 



Bv REGINALD A. R. BENNETT, M. A. (Oxon). 



CONSTRUCTION OF THE TANK ITSELF. 



When I saw the above announced as one of the sub- 

 jects for the forth-coming competitions, I at once made 

 up my mind to send in a series, and hope for the prize, 

 for the "E. M." has been an old friend to me for many a 

 long year, and I have all the back volumes from the very 

 beginning arranged on my bookshelf. I cannot truly 

 say that I took it in from the beginning, the first num- 

 bers having been presented to me some years after- 

 wards ; but, no doubt, I should have taken it when it first 

 came out had it not been for tlie fact that the first num- 

 bers appeared during the same year that I myself burst 

 upon this lower sphere, and at that time I was more in- 

 terested in the maternal lacteal fiuid than even in the 

 advance of science. However, later volumes have been 

 of invaluable service to me, and this is by no means the 

 first time that I have written in "Ours," though not be- 

 fore in the form of an article. 



As I see tliat there has been some discussion as to the 



