THE MICROSCOPICAL PREPARATION OF INSECTS 219 



SOME NOTES ON THE MICROSCOPICAL 

 PREPARATION OF INSECTS. 



By L. H. Hum, Department of Agricultural and Forest Entomology, 



Edinburgh University. 



I HAVE for some years past devoted considerable time and 

 attention to the making of entomological preparations for 

 the microscope, mainly with a view to teaching purposes. 

 As in each case I endeavoured to show up the required 

 characters in the best manner possible, I frequently 

 submitted my specimens to several methods of preparation 

 in order to find one entirely satisfactory. Perhaps some of 

 the practical experience I have thus gained may be of use 

 to other workers. 



The commonest method of preparation of whole insects 

 is that of making " transparencies," i.e., the dissolving away 

 by means of caustic potash or soda the internal tissues 

 of the insect, leaving the chitinous exo-skeleton to be 

 mounted in balsam, as a more or less transparent prepara- 

 tion to be examined by transmitted light. This is a simple 

 method with which even a tyro is not likely to have many 

 failures, though he will find that the strength of the KOH 

 solution, and the time required for treatment with it, will 

 vary with the species of insect. Fresh insects are cleared 

 rather more quickly than those preserved in spirit or 

 formalin. These must have the preserving fluid washed 

 out by soaking in water, into which insects preserved in 

 alcohol may be introduced more or less gradually. I give 

 the following method as a sample for insects that have been 

 preserved in 80 per cent, spirit : 



Remove the specimen to 50 per cent, alcohol. 



Substitute plain water to remove all traces of alcohol. 



Boil in 10 per cent. KOH solution for fifteen minutes (more 



or less according to species). 

 Wash thoroughly in distilled water. 

 Float the insect, if an adult with long appendages, on a 



