l893-] NEW-YORK MICROSCOPICAL SOCIETY. 93 



frustules taking the stain in such a dense and beautiful manner, 

 that there must have been an infinitely thin layer of protoplasm, 

 which appropriated the dye. My reason for this conception is, 

 that in the two slides of the Montgomery, Ala., fossil fresh-water 

 earth, which also form a part of the series of slides, the silica, no 

 longer having any plasmic coating, refused to take the aniline dye, 

 except in a manner to be referred to further on, the plain surfaces 

 separating the lines of ribs being almost devoid of any show of 

 stain. The above is about all of interest that I could determine 

 as to the effect of an aniline dye on the living frustules. 



The bottles containing the living diatoms from Whistler, as 

 well as the fresh brackish-water material from Mobile Bay, were 

 allowed to remain over-night on the mantel near the window. 

 On the next morning I observed the contents of the two bottles 

 with a band lens, and noted that hundreds of the Whistler dia- 

 toms had left the sediment and algae at the bottom, and were 

 travelling around near the line of the surface of the water in the 

 bottle in preference to any other part of the sides. At this mo- 

 ment I recalled the common statement that diatoms, as well as 

 desmids, will congregate at the lighted side of the vessel holding 

 the mud with which they are mingled. To verify this I success- 

 fully used the following expedient: Thrusting the bottle previously 

 described tightly down into a parlor match-box, I cut a hole in 

 the paper of the box, a quarter of an inch in diameter, at a point 

 about the middle height of the fluid, and on the reverse side I cut 

 a similar hole, taking care not to detach the pieces of paper, so 

 that they might be opened and shut as little windows, so as to 

 admit transmitted light through the fluid on subsequent examina- 

 tions. Having done this, I excluded all light from every part 

 of the bottle, except from the central quarter of an inch hole. 

 When this was done I exposed the bottle to the diffused light of 

 the day, toward the south, and at convenient intervals during the 

 daylight, for the balance of the day, I observed such changes as 

 went on at the orifice admitting daylight. 



The first phenomenon of interest, after about one hour's ex- 

 posure, at about 9:30 a.m., was that the diatoms had already 

 congregated at the spot of clear glass in fair numbers and were 

 travelling across the field in all directions, with an easy, steady, 

 direct motion. There were also groups of the " tetradelphia" 



