344 J. B. SCRIVEN ON PREPARATION OF SERIAL SECTIONS OF INSECTS, 



larva. The pupa also should now be put into methylated spirit, 

 and, if it be five days or more old, a small opening may be 

 made in the shell after about four hours, and it may be again put 

 into the same medium. 



Next day the shell can be removed, and a slice taken off the 

 nymph, which should now, as in the case of the maggot, be put 

 into absolute alcohol for three days. 



If the pupa is younger, and the shell adherent so that it cannot 

 be separated, the whole may be cut through after twenty-four 

 hours in the methylated spirit, and then dropped into absolute 

 alcohol. 



The imago (which ought to be a newly-hatched one) should not 

 be boiled, but at once put into methylated spirit. In twenty- four 

 hours it also may be cut through, and dropped into absolute alcohol. 

 As soon as this has been done, the nymph, or imago, should have 

 its air exhausted by an air-pump or exhausting syringe ; otherwise 

 cavities may remain, even after imbedding.* 



2. Imheddhig. — If the specimen is to be stained on the slide, it 

 is now ready for imbedding ; if to be stained in bulk, this is the 

 time for it, and it must be dehydrated again afterwards. In either 

 case, when the hardening has been sufficiently carried out, it 

 should be placed in about one fluid drachm of absolute alcohol in 

 a small capsule on the water oven, and heated to the melting 

 point of the imbedding medium, which ought to be kept liquid on 

 the same oven. The specimen may then be transferred direct to 

 the melted medium with an ordinary lifter. No intermediate 

 process, such as soaking in ether, chloroform, or cedar oil, is 

 necessary or desirable. It must be kept in the melted material 

 till bubbles of spirit, if there be any, have ceased to rise : an hour 

 may be enough, but 2^ hours is a safer time. Often no bubbles 

 are visible from first to last. 



As an imbedding medium pure paraffin has found most favour 

 with microtomists. Professor Bolles Lee says it is better than 

 " any of the many mixtures with wax and the like that used to 

 be recommended. "t Its tendency, however, to form vacuoles in 

 cooling is to my mind a great objection, as these often injure greatly 



* Dr. Lowne says that latterly he has not used the exhausting syringe 

 (" Anatomy and Morphology of the Blowfly," p. 860). 

 ■j- " Microtomists' Vade Mecum," 5th edition, p. 115. 



