Regeneration ni Compound Eyes of Crustacea 167 



material. Among those most frequently used were Fleming's 

 osmic fixative, Perenyi's fluid, Kleinenberg's picro-sulphuric, 

 picro-aceto-sulphuric, Petrunkewitsch's fluid and alcohol acetic. 

 Other fluids also were used and boiling water was tried. The 

 best results were obtained from picro-aceto-sulphuric and Perenyi's 

 fluid. In any case it is difficult to obtain a fixative that does not 

 shrink the inner tissues from the chitin, the regenerated tissues 

 being much more easily affected in this respect than normal 

 tissues. 



The embedding was done altogether in hard parafline 54° to 

 58° C. melting point. It was necessary to embed the material for 

 a long time in order to cut it without tearing the chitin from the 

 softer tissues. The most satisfactory infiltration was obtained by 

 placing the objects first in equal parts of oil and parafl&ne, leaving 

 them on top of the water bath over night and then replacing the 

 oil and paraffine with pure parafl&ne, leaving them on top of the 

 water bath from eight to ten hours longer. Finally they were put 

 in the paraffine bath from one to two hours. Even after the most 

 thorough infiltration it was well nigh impossible to obtain complete 

 series of good sections, because of the difficulty of cutting through 

 the different textures of the material. In dehydrating preparatory 

 to embedding, cedar or bergamot oil was usedin preference to xylol 

 as these oils made the tissues less brittle. 



The chief stains employed were Fleming's triple stain and 

 Heidenhain's iron haematoxylin. Various counter stains were 

 used with the iron haematoxylin but the most generally satisfactory 

 were acid fuchsin and orange G. 



In most instances no attempt was made either to soften the 

 chitin or to remove the pigment before the eyes were sectioned. 

 As a rule, however, the material was fixed shortly after a moult so 

 that the chitin was as soft as could be obtained. Any sort of a 

 reagent used to soften the chitin seemed to be more or less inju- 

 rious to the softer parts, particularly the regenerating tissue. 

 When the chitin was removed, however, 2 per cent nitric acid in 

 70 per cent alcohol was found to be most satisfactory. It was 

 generally disadvantageous to remove the pigment because this 

 destroyed many of the landmarks both in respect to the regener-. 



