SOLLITT, ON STRIDE OF DIATOMS. 49 



bring them out, and I have little hesitation in stating that 

 the stria? on this diatom vary from 65 in the T^^th °f an 

 inch up to a degree of fineness which no lenses that we now 

 have will show. I have always found the various kinds of 

 Nitzschia to be the most irregular in the number of their 

 striae in the inch, of any Diatomaceae that I have studied. 



The Navicula rhomboides is another instance of the impos- 

 sibility to give correct measures of the number of stria? on 

 any diatom. Our American friends have set the number 

 down at 70 in the j-^Vfith of an inch, Smith says 85. 

 I have one or two specimens of this diatom that have 

 not more than 60 in the yaW- I have others, again, so fine 

 as to defy all means of showing the striae on them, and those 

 all in the same slide and of the same gathering. I could, 

 if necessary, apply similar observations to all the different 

 diatoms of which our American friends have given us the 

 measurement. Had they been acquainted with those facts, 

 I think they would never have published what they evidently 

 consider their standard of correctness, nor would they have 

 tried to prove that all other observers except themselves were 

 in error. 



Nothing leads to such great mistakes in scientific inquiry 

 as too hasty conclusions. I consider that all their measures 

 are correct, as far rs they have gone. They have played the 

 air ver\ well, but they have neglected the variations. 



I may further observe that our American friends are not 

 to come to the conclusion that all the measures given in 

 Smith's " Synopsis" are his own, as I know for a fact that 

 many of them were communicated to him by others. He 

 was a most indefatigable observer; but one man cannot do 

 everything, and the great wonder is the correctness of most 

 of the measures which he has given for diatoms of a medium 

 size. 



I now come to Messrs. Sullivant and Wormley's remarks 

 on the Amphipleura pellucida. They say, "We have not 

 been able even to ' glimpse' the striae on this diatom. Messrs. 

 Harrison and Sollitt, in their paper above cited, estimate 

 the striae at 125 to 130 in the -r^th of an inch." They 

 further add : " In conclusion, we may remark that our ex- 

 periments are confirmatory of the generally received opinion 

 that striae closer than about 85 in the t^Vit have not yet been 

 resolved." In their measurement of those diatoms the striae 

 of which they have been able to see, 1 have no doubt of their 

 general correctness; but their remarks on the A. pellu- 

 cida put me in mind of the fine double star, »j Corona, 



VOL. VIII. K 



