162 



JOURNAL OF THE 



[December, 



were of normal size and form, and appeared to be in the best 

 condition. On reflection, I attached much importance to this 

 negative result, for it impressed me with the conviction that 

 the diatom seed was so exceedingly small that all of it, practi- 

 cally, passed through the filters used. 



Through all these experiments excepting No. i and No. 2 of 

 the first series, one is struck with the apparent discrepancies, 

 differences in the amount of the several crops, in the species 

 and in the sizes of individuals of the same species. The diatoms 

 in experiments No. i and No. 2 of the first series, must, I 

 think, be considered normal, and I give herewith a table of 

 measurements, in parts of an inch, of individuals of the three 

 genera contained in each of the jars used in those experi- 

 ments. 



Amphora. 



Navicula. 



LONG. 



THICK. 



LONG. 



THICK. 



The Navicula column shows much diversity of sizes, and yet 

 the diatoms whose measurements are there given were of the 

 same species as those in jar C of the second series, which showed 

 complete uniformity in size. As to the Figures i, 2, and 3 in 



