189S.] MICEOSCOPICAL JOURNAL. 113 



stand it, none of those slides are now in the market, nor will they 

 be until after thev have been exhibited in some of the principal 

 cities of Europe and of tliis country. If some of our diatom ex- 

 perts would only put up such slides of some of the most beautiful 

 forms of the polycystina, I am sure they would find a ready sale. 

 I have a slide with just one specimen of Astromma on it, put up 

 by Mr. Geo. B. Scott, and it is ''a thing of beauty and a joy 

 forever," never failing to call forth admiration. It happens to be 

 quite a large form, and here let me say that the Radiolaria vary 

 considerabh' in size. I have just measured a dozen or so of them 

 and find that the round forms, spheres, or disks, range from i-S5th 

 to i-300th-inch. This, of course, is w^ithout taking into account the 

 spines, some of which are as long as the diameter of the main 

 skeleton and even longer. In the conical forms, the long diam- 

 eter, exclusive of appendages, horns, or feet, ranges from i-9oth to 

 i-400th-inch. while the double forms have a length of from i-40oth 

 to J-7ooth-inch. Uistiasfrzrm^ including the arms, measures 

 r-4qth-inch. 



( To be continued.) 



How to Collect Desniids. 



By WM. N. HASTINGS, 



ROCHESTER, N. H. 



Desmids are microscopic unicellular fresh-water plants, and be- 

 long to the order Algae. Under favorable circumstances the 

 largest of them may be seen by the naked eye as minute green 

 specks in the water. The smallest of them require a good com- 

 pound microscope for identification, being of no greater diameter 

 than a human blood corpuscle. The}^ difier from diatoms most 

 strikingly in the cell-wall being soft, and it is said to be composed 

 almost wholly of cellulose (the material of cotton), while the cell- 

 wall of diatoms is infiltrated with silica (the material of glass), 

 w'hich renders them brittle. From other algte they are chiefly 

 distinguished by each cell being composed of two svmmetrical 

 half cells joined at their bases, w'hich are sometimes so much 

 constricted as to appear to be two cells, but as the protoplasm 

 (bioplasm or life substance) circulates from one to the other they 

 really form but one individual cell. Desmids differ from one an- 

 other in shape, size, markings, and the presence or absence of 

 processes, angles, spines, etc. Over thirteen hundred of them 

 have already been described, and while it seems really wonderful 

 that so many and beautiful forms can be fashioned from a single 

 cell, the student will readily understand that the possibilities are 

 almost infinite. Desmids have a small power of motion, which 

 is usually so slight as to escape observation, but it is sufficient to ex- 

 tricate them from sediment when they are not too deeply buried. 

 By secretion of a sort of mucus they are able to anchor themselves 



