XVI 



TECHNIQUE 



Except when timed stages were desired, a frame of brood comb, 

 containing a considerable number of eggs was selected. The eggs 

 were then lifted out of the cells and transferred singly to the 

 fixing fluid. A small fine-pointed brush, slightly moistened, 

 was found most convenient for this purpose. Other inves- 

 tigators have made use of a bent needle, but with this instrument 

 there is considerable danger of damaging the rather delicate egg. 

 A considerable difference was noted between different lots of eggs 

 in regard to the ease with which the eggs could be removed. In 

 some lots a light touch with the brush was all that was needed 

 to loosen the egg from its attachment to the bottom of the cell, in 

 others the eggs were stuck so tight as to require considerable 

 manipulation to bring them out of the cells without damage. 

 Although no records were kept it seems not unlikely that this 

 difference in the adhesiveness of the eggs was traceable to a differ- 

 ence between the mother insects, the queens, some secreting more 

 adhesive, or else of a better quality, than others. 



Five fixing fluids were used : Bouin's picro-f ormol, one-half 

 to eighteen hours 25 ; acetic-alcohol (Carney's second formula), 

 one-half to one hour; Gilson's mixture, twenty- four hours; Pet- 

 runkewitsch's modification of Gilson's formula, twenty-four 

 hours; and Kleinenberg's picro-sulphuric mixture, three hours. 

 The last named was used but little. All of the others gave many 

 satisfactory preparations and some superlatively good ones. In 

 quality of the fixation, as regards the tissues of the embryo, there 

 is little room for choice. The effect of the different fixing fluids 

 on the yolk is however quite different. This has been described in 

 the chapter on the organization of the egg (p. 12). The effect 

 on the cells in the yolk is likewise different, eggs fixed with picro- 

 formol showing these to the best advantage. The question as to 



25 The best material came from lots of eggs left in this for five to six 

 hours or longer. 



251 



