THE MICROSCOPICAL PREPARATION OF INSECTS 229 



Dr Gustav Mann suggested to me the following plan for 

 embedding insects with tough integuments. I have not yet 

 had occasion to try it : 



Dehydrate thoroughly. 



Place in | per cent, celloidin in ether, and alcohol amylacetate 



equal parts for two days. 

 Transfer to pure chloroform to harden the celloidin (three 



changes). 

 Saturate gradually with paraffin in ordinary room temperature, 



then at 40 C, then at 60 C. 

 Very gradually evaporate the chloroform. 

 Cut as paraffin sections. 



This method has the additional advantage that it does 

 not require a paraffin " incubator." 



A simple method for pure paraffin embedding, in the 

 absence of an incubator, is given in Stephen and Christopher's 

 Practical Study of Malaria. The " embedding apparatus " is 

 simply " a slab of copper 12 x 3 x \ ins. Heat this at one end, 

 and place the vessel containing the paraffin at a point on the 

 slab where the paraffin is just kept melted. This is the 

 temperature for embedding. This simple device serves all 

 the purpose of an elaborate paraffin oven." I am using it 

 constantly now for embryological work, and have not had 

 a single failure in embedding the insects' eggs. The 

 specimens must be watched all the time of course about 

 half-an-hour in my experience but probably this time 

 might safely be shortened. 



Obviously this paper does not profess to be more than 

 a sketch of some of the chief methods employed, and an 

 indication of some of the pitfalls to be avoided. Every 

 worker on special lines evolves adaptations of method suited 

 to his specialty. It has been my own good fortune, through 

 the kindness of Dr Stewart MacDougall, to enjoy exceptional 

 opportunities of handling a large and varied material. 

 Possibly these notes may prove useful to others, whose 

 specimens of valued forms may be none too abundant. 





