WALTER] CLASPING ORGANS IN HYMENOPTERA 67 



III. Material and Methods 



In my investigations I used dry, spread, material as well as mate- 

 rial preserved in liquids ; the former for surface preparations of 

 entire wings and for sections in celloidin, the latter' for the thin 

 paraffine sections necessary for a detailed study under higher powers. 

 Surface preparations are easily made by simply inclosing the en- 

 tire wings in Canada balsam. To remove the air retained in the 

 veins, which is very disturbing, it is advisable to boil the wings in 

 chloroform before mounting. If this be done until no more air bub- 

 bles escape from the cut ends of the veins, and the wings are then 

 immediately transferred to the balsam, the veins will be found free 

 from air. To obtain sections 20 to 30 microns thick, showing the mode 

 of connection between the fore and hind wings (pi. ix), I had to em- 

 bed in celloidin, because paraffine wing-sections of this thickness fall 

 to one side as soon as the paraffine is dissolved, the wings being very 

 thin. The celloidin, of course, keeps these high sections, standing on 

 edge, securely upright. The objects destined to be embedded in cel- 

 loidin were treated in the following manner: The insect, killed in 

 fumes of chloroform or cyanide, with the wings hooked together, was 

 carefully spread and, according to its size, was dried for a half or a 

 whole week. Then I removed the two wings, still hooked together, 

 along with the accompanying part of the thorax, boiled them in chlo- 

 roform, and brought them through absolute alchohol, ether and alco- 

 hol, and ether into celloidin. Standing proved superfluous in my cel- 

 loidin sections. For the study of finer details, particularly the linking 

 of the hooks and hairs, thinner stained paraffine sections are necessary. 

 The most favorable specimens for this kind of examination are the 

 still soft and pliable wings of young, newly emerged imagos. I fixed 

 wings of this kind with good success in alcohol and sublimate and also 

 in 4 per cent formol, and preserved them in 70 per cent alcohol. The 

 chitin of the wings in older individuals is very hard and brittle, 

 splinters in cutting, and rarely yields good sections. I tried several 

 times to soften hard chitin by means of diluted nitric acid, Javelle 

 water, and caustic potash, but had no success worthy of note. A 

 relatively good method of making hard chitinous parts somewhat 

 more pliable is the one used by Hoffbaner (1892, p. 583), of allowing 

 the wings to remain in paraffine a long time. The best stains for the 

 paraffine sections proved to be concentrated aqueous solution of eosin 

 and concentrated alcoholic solution of safranin, which were taken up 

 fairly well by the chitin. Hematoxylin (Delafield's) rendered good 

 services in the staining of pupal wings. 



