THE PRESERVATION OF SPECIMENS. 311 



to keep such bottoms from swelling and shrinking with variations 

 in the moisture of the atmosphere. The result is that cases with 

 wooden bottoms are very liable to have cracks in them which will 

 give the museum pests a chance to enter. With the ordinary 

 method of lining insect cases with cork the wooden bottoms admit 

 of the cork being easily fastened in place with tacks ; but with the 

 method of arranging insects upon blocks described below there is 

 no occasion for fastening anything to the bottom of the case. 

 Hence glass can be used as well as wood, and with glass for both 

 top and bottom a case can be easily made which shall remain as 

 tight as when new. 



The Block System of arranging Collections. — The 

 ordinary way of arranging entomological collections is to pin the 

 specimens into cork fastened to the bottoms of the cases, and this 

 method will probably be found most practicable for the greater num- 

 ber of teachers that use this book ; but where a large and rapidly 

 growing collection is to be cared for, the block system of arranging 

 collections, devised by the writer, will be found much more convenient. 



Under the old system, a very large proportion of the time of a 

 curator of a rapidly growing collection is devoted to the rearrange- 

 ment of his collection, to simply removing pinned specimens from 

 one place in a cork-lined case and putting them into another. This 

 not only consumes much time, but results in the breaking of many 

 specimens. Where the block system is used this loss of time and 

 breakage of specimens is reduced to a minimum. 



The fundamental idea of the block system is to fasten upon a 

 small block each series of specimens illustrating a single species. 

 A standard size of block is adopted for what may be termed the 

 unit block; other blocks which are multiples or fractions of this 

 size are also used. When it is necessary to rearrange the collection 

 the relative positions of the blocks can be easily and rapidly changed 

 without danger of breaking the specimens. 



The blocks are made of soft nonresinous wood and are painted 

 on the upper side with the zinc-white and glue mixture described 

 above. The pins are inserted and removed with pinning forceps or 

 pliers. It is desirable to have a few blocks made of compressed 

 cork or of wood with sheet-cork or linoleum tacked to them for the 

 specimens that are being studied or are not yet classified. When 



