290 Kobcrt Wilhelm Hefner. 



to^ 



VI. Matp^rial and Methods. 2 



The eggs of Chrjsomelid beetles are usually laid on the leaves 

 of the plants, which serve as food for the larvfe. Callagraplia nmlti- 

 punctaia deposits its eggs in batches of from two to twenty on the 

 under surface of willow leaves (8aUx longifolia). A number of 

 these beetles were kept in stender dishes and their eggs as soon 

 as laid were transferred to watch glasses. All the eggs laid at one 

 time were found to be in practically the same stage of development, 

 and the batches were, therefore, carefully separated from one another. 

 The age of the eggs proved to be no exact criterion of their develop- 

 mental progress as external factors (temperature, humidity, etc.) 

 play an important part in the rapidity of embryonic growth. Thus, 

 two eggs of the same age which are kept under different environ- 

 mental conditions, may on examination be found in very different 

 stages of development. For this reason the various embryos figiired 

 are not designated by the number of hours since the eggs were laid, 

 but are classed arbitrarily according to their stage of development. 



Eggs of Calligrapha lunata were found on leaves of the wild rose 

 (Rosa hlanda) ; those of Leptinotarsa were taken in abundance from 

 potato plants {Solamnn tuherosum). The eggs were preserved at 

 intervals of from fifteen minutes to one hour and a complete series 

 was obtained from those just laid to those containing embryos ready 

 to hatch. A few eggs of Leptinotarsa were dissected out from the 

 oviducts of the adult beetles. 



A large number of fixing fluids were tried ; the one which gave 

 the best results was a modification of Petrunkewitsch's fluid. The 

 mixture was heated to a temperature of about 80° C, and poured 

 over the eggs ; this fluid was followed after half an hour by seventy 

 per cent alcohol containing a small amount of iodine. After the 

 above fixation, the chorion stood away from the egg so that it could 

 easily be removed with needles under the binocular microscope. 

 Sections were cut 6V3 microns thick and were stained on the slide; 

 Mayer's acid-hsemalum followed by Bordeaux red, was used more 

 than any other combination, although most of the commoner methods 



=For an accoimt of tbe breeding habits of these beetles see Heguer, 1908. 



