APPENDIX TO CHAPTERS VI. TO IX. 



METHODS OF STUDY. 



No great difficulties have been experienced by me in the 

 preparation of sections of either embr\-os or nymphs, except 

 in the early stages of the pupa, when the pupa-shell cannot be 

 removed. 



The difficulty in this case arises partly from the imper- 

 meability of the pupa-shell, partly from the fact that paraffin 

 will not adhere to it, and partly from the extreme friability of 

 the sections — perhaps due to the difficulty of fixing the tissues 

 owing to the impermeability of the pupa. 



In preparing embryos, it is advantageous to remove the 

 chorion, or egg-shell, after heat coagulation, but I have pre- 

 pared ver}^ good sections occasionally when this has not been 

 done, staining them after cutting. I have found it impossible 

 to stain them in mass unless the shell has been removed. 

 Young pupae should be divided with a razor after heat coagula- 

 tion, and the extreme ends of the pupa case cut off. In pupae 

 after the third day the whole shell must be removed. 



I have found collodionising the sections advantageous in 

 young pupae. This is easily effected by painting the cut 

 surface of the paraffin block with thin collodion, which dries 

 almost instantaneously. 



As the study of the development in the egg and pupa necessi- 

 tates the preparation of a large number of sections, the process 

 of staining these after they are cut, although it gives the best 

 results, is far too laborious ; it is necessary, therefore, to have 

 a good method of staining en masse. 



