H. MORLAND ON DIATOM STRUCTURE. 307 



valves remaining of those I Lad already picked out. It is a rule 

 of mine when mounting tl selected " diatoms, if I find them in 

 any way dirty, to wash them by passing them in and out of a drop 

 of water on a glass slip. I was doing this with these diatoms 

 and as they were drying, concave side downwards (and consequently, 

 holding down tight on the glass slip, like suckers, as it were), 1 

 touched them slightly with my mounted bristle, and found that, 

 with very little trouble on my part, I could remove nearly the 

 whole of the upper and outer structure of the valve, which appeared 

 to me as if it were rotten ; I took advantage of this circumstance, 

 and in a ver\ short time prepared a number of valves meeting my 

 requirements. In due course my correspondent received a slide of 

 these " tampered with " diatoms from Tampa Bay, with which he 

 was very well pleased. I may say that this material also contains 

 Enpodiscus radiatus, Bailey, which appears to be similarly affected 

 in the outer substance of the valve, but I have not yet either 

 mounted it or given it a proper examination under the microscope, 



I should just like to ask one question, viz. : How many hoops 

 does a frustule of Pleurosigma have ? In washing such a frustule 

 (which has broken up at once on being drawn or pushed out of the 

 water) I have observed quite a number of hoops peeling off one 

 after another. I think that many persons must have noticed an 

 extraordinary number of hoops on some of their slides of Pleuro- 

 sigma3, in fact, more hoops than valves. 



In conclusion I will venture to remark that it is not always the 

 best workers that have the longest purses, and as the examination 

 of the structure of diatoms requires a somewhat high power, it is 

 possible that some such workers may feel a little discouraged and 

 unwilling to undertake the study of this branch of microscopy. 

 To these fellow- workers I have a word of comfort, and that is that 

 the cost of a suitable objective is not quite so high as they may 

 probably think ; my highest objective is only a Zeiss's Gr water- 

 immersion, which cost me £5 10s., and is really a very nice lens, 

 giving a power of over 1,000 diameters with a " D " eyepiece of 

 Swift's. There is still a further comfort for some of our poorer 

 members ; I understand that a new optical glass has lately been pro- 

 duced which will throw all lenses hitherto manufactured completely 

 into the shade. This may possibly cause a number of -^ inch oil 

 immersion lenses of 1*43 N.A. to be disposed of at an alarming 

 sacrifice. I should like then to pick up one for a five-pound note. 



