322 
larva in the dorsal middle line, where there are very few tracheæ, 
pressed both sides outwards and sealed them on to the glass by 
means of the picein, which was gently heated for the purpose. As 
shown by fig. 2 this method can give a very good view of the 
whole tracheal system, but of course the mounting and the way 
of opening the animal must depend upon the structures which it 
may be especially desired to bring in view. 
When the tracheal system alone is the object to be exhibited 
the other tissues or the greater part of them can be removed by 
digestion: The mounted preparation is placed in water to which is 
added about 0.5 per cent hydrochloric acid (1 cc concentrated HCl 
to 100 cc water) and V 2 to 1 per cent commercial pepsin. The 
digesting mixture with the preparation is placed at a high tempe¬ 
rature (25 ^—35 ^). After some two to three hours and at suitable 
intervals afterwards, according to the progress of the digestion, the 
preparation is taken out, placed in cold water and washed gently 
under a tap. By this means the digestion can be discontinued at 
any desired stage, and the finished preparation can be mounted in 
a weak formaline solution — not of course in alcohol. The alkanna 
dye will not stand strong ligt, but otherwise the preparations ap- 
pear to be durable. Fig. 2 shows an injected specimen of the larva 
of Cossus ligniperda. I am much indebted to Prof. Wall engren 
of Lund for the photograph. 
26-4-17. 
