312 ENTOMOLOGY. 



posterior wall of the cranium of the fresh insect and then to expose it 

 to the fumes of 1 per cent osmic acid solution for forty minutes, then 

 to wash in 60 per cent spirit for a few minutes, and finally to harden 

 in absolute alcohol. Crania thus prepared may be cut into fine 

 sections by the automatic microtome, and stained in hsematoxylin or 

 borax-carrniue. With most insects, however, I have found it im- 

 possible to use this microtome, owing to the hardness of the chitin of 

 the cranium and of the mouth-appendages. In such cases I have 

 used a Jung's microtome, with the razor set so as to give a long 

 sweep at each stroke, and the sections carefully removed from the 

 razor, and mounted one by one. 



"I have tried various methods for depigmenting the eyes, such as 

 bleaching-powder, nitric acid, chlorine, etc., but the best is that of 

 exposing the sections when cut to the action of nitrous fumes. This 

 is done in the following mariner: The sections are fixed in position 

 on the slide by Mayer's albumin and glycerine solution, and when 

 the paraffine has been removed by turpentine and the turpentine 

 driven off by absolute alcohol, the slide is inverted over a capsule 

 containing 90 per cent spirit, to which a few drops of strong nitric 

 acid have been added.* Copious nitrous fumes are given off and the 

 pigment dissolves. The action can be stopped at any moment by 

 washing with neutral spirit, and when the washing is complete the 

 sections can be stained in haematoxylin or any other solution. 



" For teasing the best solution is chloral hydrate. I leave the eye 

 or optic tract in 5 per cent solution of chloral hydrate for twenty- 

 four hours, and then tease with needles and mount in glycerine. In 

 some cases I have made very satisfactory preparations by fixing the 

 teased tissues to the slide with albumen and glycerine solution and 

 then washing with spirit and staining in .the ordinary way, or stain- 

 ing after depigmentiug with nitrous fumes. 



"I have tried various kinds of hsematoxylin stains, but the solu- 

 tion which gives the best results, and is in every way the most satisfac- 

 tory, is one which I have made by following Mitchell's instruc- 

 tions, with a few additional precautions. I will describe here the 

 mode in which I now make hoernatoxylin stain: Take 56 grams 

 of the logwood extract and thoroughly pound it in a mortar. Then 

 place it on a filter, and pour about a litre and a half of ordinary tap- 

 water through it. The filtrate may be thrown away and the residue 



* Prof. Grenacher, according to Carriere, besides one with nitric 

 acid, employed the following mixture : Glycerine, 1 part ; alcohol 

 (80 per cent), 2 parts ; and hydrochloric acid, 2-3 per cent. The 

 preparation remains in this mixture until the pigment changes color 

 and becomes diffuse. (Arner. Naturalist, 1886, 89.) 



