POSITION OF OBSERVER. 251 



look at diatoms, and quite another to study them with 

 the especial object of becoming acquainted with the 

 behavior of the objective, while it must be admitted 

 that there is a fascination and charm per se 9 connected 

 with diatom examinations under the microscope. It is- 

 equ.dly true that the student can use them legitimately 

 and for the purpose named, without establishing any 

 claim to the functions of the diatomist. 



Referring to the especial purposes we have been con- 

 sidering, the following list of objects will amply suffice, 

 for the study of the one-sixth or one-tenth objectives,, 

 viz: 



1. Navicular Rhomboides, Monmouth, Maine, Balsam Mount 



2. Navicular Rhomboides, Cherryfleld, Balsam Mount. 



3. Erustulia Saxonica, Leipsig, Germany, Balsam Mount. 



4. Frustulia Saxonica, Isle of Shoals, U. S., Balsam Mount. 



5. Amphipleura Pellucida, Bridge of Allan, Scotland, Balsam 



Mount. 



6. Amphipleura Pellucida, Aberdeen, Scotland, Balsam Mount. 



7. Surriella Gemma, Balsam Mount. 



Of the above list, Nos. 1 and 2 can readily be ob- 

 tained of the dealers. As to the others named, Prof. 

 H. L. Smith, of Geneva, .N. Y., has a large supply of 

 the material, and has kindly supplied the author and 

 his friends with excellent mounts and at figures much 

 below the usual list prices. 



In addition to the diatoms, a genuine mount of 

 English podura will be a capital thing to have on hand 

 for occasional comparisons, but the student must on no- 

 account select the slide himself. Poor scales are simply 

 good for nothing, while perfect ones are held by the 

 opticians in the highest esteem, and are constantly used 



