10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 



acetate sheeting. Cover glass is best cut with a diamond point ; a 

 small chip cemented to the end of a drawn-glass tube makes a perfect 

 instrument for the purpose. The slip may be cut to the required size 

 after the specimen or series has been attached to it. It is imperative 

 to work on a perfectly smooth, level surface, preferably plate glass ; 

 and to use a rule which will not slip, such as a microscope slide faced 

 on one side with adhesive tape. The best adhesive for mounting on 

 glass is acetate cement thinned with ethyl acetate. A generous appli- 

 cation of a slightly thicker mixture should be used to attach two 

 narrow strips of bond paper or single-ply bristol board (about -J inch 

 wide for small slips), one on each side of the glass along the entire 

 rear margin of the mount. Approximately half the width of these 

 strips should be occupied by the glass between them, the other half 

 being left for direct contact of the strips and subsequent perforation 

 by the mounting pin. The strips should be gently pressed together 

 and carefully aligned. When working with a quantity of material 

 of fairly uniform size, a number of sHps can be attached at intervals 

 to a long bottom strip, and a top strip of equal width can then be 

 cemented over the whole. After 15 minutes or so of drying, before 

 the cement has become thoroughly hardened, the mounts should be 

 cut apart, the paper trimmed close to the glass with fine scissors, and 

 each mount carefully pinned on a flat-topped, gauged block, prefer- 

 ably slotted (VI) (fig. 4). It is advisable to pin the mount tilted 

 slightly upward, and to immobilize it with a drop of cement deposited 

 on the bottom strip around the pin. 



A well-constructed cover-glass mount is neat, strong, and optically 

 ideal. However, unless its specimens have been exceedingly thor- 

 oughly degreased, it may, in time, collect fine droplets of oil emanat- 

 ing from them. Cover glass is, therefore, best employed in mount- 

 ing small specimens (10 mm. or less) which can easily be cleaned of 

 all grease. 



The writer has experimented with a variety of materials for the 

 supporting strips of these mounts. None of the transparent "plastics" 

 and celluloids used has proved so efficient as heavy paper. Besides 

 its stability, another advantage in the paper base is that it can effec- 

 tively serve to display data, numbers, etc., written thereon. 



V. DIRECT PINNING 



Provided specimens are of sufficient size to justify impaling them 

 on insect pins, they can always be effectively mounted in accordance 

 with this standard technique. It should be pointed out, however, that 

 substituting direct pinning in the larger forms for the transparent- 



