CHAPTER II 



THE LARVA OF CHIRONOMUS 



I. External form. 

 Many external features of tlie larva can be made out Method of 



examina- 



witli the lielp of simple lenses, magnifying from five to tion. 

 thirty diameters, but the details require the compound 

 microscope. Larvae are easily killed by placing them for 

 a few seconds in water heated till it feels hot to the 

 finger. Then they may be placed in water on a glass 

 slip, and covered with a glass circle. It is often desirable 

 to take off the weight of the cover by cotton-wool or three 

 small glass beads. When it is desired to examine a larva 

 alive, small specimens, not more than half-grown, are to 

 be preferred. A little cell is made of cotton-wooi ; this is 

 filled with water; then the larva is picked up with a clean 

 brush, and dropped inside the cell ; lastly, a glass cover 

 is gently lowered upon it. The cottcn-wool keeps off the 

 pressure of the cover, and also restrains the movements 

 of the larva. The space enclosed by the ring of cotton- 

 wool should be clear of threads or nearly so, in order that 

 the object may not be obscured. The beating of the 

 heart, the contractions of the intestine, the action of the 

 jaws, and many other operations of the living animal can 

 be conveniently studied in this way. The details of the 

 larval head can be made out by treating the parts with 

 caustic potash. Soak several heads in a ten per cent, 

 solution for two or three days, wash thoroughly with 

 water, and mount in glycerine, or (after dehydration) in 



