THE VICTORIAN NATURALIST. 105 



last April near Geelong, and are living in a tumbler of sea water. 

 Wlitrn first placed in this tumbler they were, of course, mixed up 

 with the mud in which they were found. The latter having 

 settled in the course of a day or two, the diatoms could be ob- 

 served as a dark olive coloured film upon its surface, and during 

 daylight could always be seen in this position. After a time 

 it occurred to me to examine them after nightfall, and I was 

 much surprised to find they had all disappeared beneath the 

 surface of the mud. Examination on successive days showed 

 this disappearance to be of regular occurrence from day to day. 

 After the lapse of a few days I placed the glass on a ledge against 

 the garden fence, shaded from the sun, and on the following day 

 noticed my friends had not come to the surface as usual, the day 

 being fine, but dull and cold. The same conditions prevailed on 

 the succeeding day, the diatoms still keeping below ; but on the 

 third day, which was warm and clear, they came to the surface as 

 before, and could easily be seen with a pocket lens actively 

 sliding over each other and up the sides of the glass to the surface 

 of the water. After repeated observations I have noticed that their 

 movements in an even temperature, and screened from direct sun- 

 light, are fairly constant and regular — that is, they come to the 

 surface during daylight, and at night disappear among the 

 surrounding mud, making their way usually right to the bottom 

 of the glass. If exposed to any marked change of temperature 

 they appear to be at once affected thereby, remaining imbedded 

 in the mud for days together, provided the cold continues, even 

 though the sky may be bright and clear. I may remark that 

 although limited to not more than a quarter of a pint of sea water 

 they appear both as healthy and numerous as when first placed 

 therein. I tender these observations merely in the hope that they 

 may be useful and suggestive to others. No one seems to have 

 studied very carefully the effect of light and heat upon these low 

 forms of life, or, at least, no record of such observations has come 

 before my notice, although it has often been noted that diatoms 

 rise to the surface of any water containing them, being carried 

 thither apparently by the gases they evolve when exposed to 

 bright sunshine. 



Our time will not permit of any further reference to these at 

 present unsolved problems ; nor yet to the interesting, but inter- 

 minable, controversy as to the nature of the fine sculpturings, or 

 markings, as they are more generally termed, upon the surface of 

 the valves. 



I am the rather desirous of giving you something more prac- 

 tical in the shape of my own experience, such as it is, upon the 

 various methods of collecting, cleaning and mounting diatoms. 

 And, first, as to their collection. — Diatoms are, I need scarcely say, 



