No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 141 



Method II. — The hardened eggs or embryos, freed from 

 their envelopes, are transferred from seventy per cent alcohol 

 to Delafield's or Ehrlich's hasmatoxylin, in which they are left 

 not longer than thirty or forty seconds. Then they are suddenly 

 returned to seventy per cent alcohol, and a drop of twenty per 

 cent HCl is allowed to fall through the alcohol onto the em- 

 bryos, which almost instantly change color. As soon as they 

 pass from a red to a salmon tint the fluid must be hastily re- 

 moved and replaced by fresh seventy per cent alcohol, to which 

 a trace of ammonia has been added. The nuclei gradually turn 

 blue and throw the embryo out in bold contrast to the pale 

 yellow yolk. In older isolated embryos, the stain faintly tinges 

 the surface protoplasm, accentuates the shadows, and leaves all 

 the sharp depressions unstained. When embryos thus treated 

 are mounted in glycerin or balsam and examined with widely 

 opened diaphragm and Abbe condensor under a moderately 

 low power (about sixty diameters), the surface relief is 

 exquisitely sharp and clear. The exact delimitation of the 

 appendages, both permanent and evanescent, the tracheal 

 orifices, oenocytic invaginations, segments of the brain and 

 nerve-cord, etc., may be traced with great precision, as the 

 figures on Plate I will testify. 



The method- here given with several modifications of my own, 

 was taught me by Dr. Wm. Patten, who has used it with great 

 success in his studies of Arthropod development, more especially 

 in his work on the brain and eye of Aciliiis. A very similar 

 method seems to have been used by other investigators {vide 

 Foster and Balfour, Elements of Embryology, 1883). Un- 

 fortunately, surface preparations with haematoxylin are not 

 permanent, probably on account of the acid used to extract 

 the stain. The color gradually fades, often disappearing 

 completely in the course of a few weeks. I therefore prefer 

 Czokor's alum cochineal, washing in water instead of acidu- 

 lated alcohol. These preparations are nearly or quite as clear 

 as the haematoxylin preparations and keep indefinitely. 



Method III. — This is really only a compromise between 

 Methods I and II. Embryos in the katatreptic stages are 

 allowed to remain in Czokor's alum cochineal till the stain has 



