94 THE LARVA OF THE BLOW-FLY. 



place of a diffuse stain, dehydration with alcohol and mounting 

 of soft tissues in Canada balsam in the place of fluids, glycerine, 

 and glycerine jelly, which all have a most destructive action so 

 far as the finer details of structure are concerned. The use of 

 serial sections stained after they are cut has almost superseded 

 the old methods of dissociation with needles, although this 

 method is not without advantages, when the tissues are 

 properly fixed. I believe I have tried all the principal methods 

 recommended at various times, but have finally adopted the 

 following almost exclusively. 



1. Fixing. — The ' fixing' of the tissue elements is of primary 

 importance, and the majority of the preparations I have seen 

 of parts of insects are rendered worthless by defective methods. 

 All the ordinary fixing fluids fail in the Blow-fly larva, owing to 

 the great impermeability of the integument. I have found the 

 following methods good : 



1. The integument may be slit up longitudinally under 

 Flemming's solution,* and the parts removed with fine-pointed 

 glass rods. Preparations of the several tissues should be 

 examined within half an hour or less of their immersion. 



2. The living larva may be injected by means of a hypo- 

 dermic syringe, with a mixture of peroxide of osmium, i % 

 solution, and absolute alcohol, i part to 20. This is the best 

 preparation for the demonstration of Newport's segment and 

 the stomal discs. Larvae so prepared may be dissected under 

 water or Flemming's chromo-acetic solution ;-f or the parts 

 removed may be placed in absolute alcohol, and afterwards 

 mounted. 



3. The larvae may be fixed by heat : a few should be placed 

 in a test-tube with water, heated to the boiling point, and 

 allowed to cool. The opacity of the larva indicates the coagu- 

 lation of its blood. Larvas heated in absolute alcohol, Mayer's 

 method,! almost always burst. Heating in water is the best 

 method of preparing larvae for cutting sections, as all the 



* Chromo-aceto-osmic mixture ; an aqueous solution of chromic acid o'25, 

 osmium peroxide 01, and glacial acetic acid o'l %. 

 t The above without the osmium peroxide, 

 t Mitth. Zool. Stat., Neapel, ii., p. 7, 1S81. 



