384 REV. EUGENE o'mEAUA. 



And here I may mention that extra thin covering glass 

 shoukl always he employedj or else it is impossihle to use a 

 very high power. Run the covering glass round with glyce- 

 rine jelly, when cold with a solution of gum dammar, and, 

 lastly, when that is hard, again Avith Bell's cement. 



I think it is as well to use layers of different varnishes ; the 

 fluid is then less likely to ooze out ; of course, in putting on 

 the jelly and varnishes, each layer should be made to 

 thoroughly overlap the preceding one. By these means the 

 preparations may be sealed up with great safety. 



When mounting in dammar the gum should not be re- 

 moved, and to prevent this spirits should be mixed with 

 the water which is used to dilute Beale's carmine fluid. The 

 sections are to be mounted in the ordinary way by macerating 

 them for a few minutes in absolute alcohol, transferring to 

 slide, evaporating alcohol, adding turpentine, removing ex- 

 cess when the tissue is clear, and finally adding the solution 

 of dammar and placing covering glass on the top. 



Before concluding, I must mention one of the most impor- 

 tant points in the whole proceeding ; it is the necessity of 

 obtaining the cochlea in a perfectly fresh state. In the 

 smaller animals, when the brain is removed, any time wdthin 

 twenty-four hours Avill do very well, but when we come to 

 the larger animals, and especially man, it is necessary to 

 remove the cochlea within ten or twelve hours after death, 

 otherwise the brain, which decomposes so rapidly and lies 

 close to the delicate structures required, hastens decomposi- 

 tion, destroying all traces of the organ of Corti. 



This has been my great difficulty with the human cochlea, 

 and I have not yet succeeded in getting it fresh enough for 

 making sections entirely to my satisfaction. 



E.ECENT Researches in the Diatomace^.^ 

 By the Rev. Eugene O'Meara, M.A. 



{Continued from page ^iQ.) 

 III. 



We come now to consider the most interesting portion of 

 Dr. Pfitzer's valuable contribution to the study of the Diato-^ 

 macea, namely, the characteristic arrangement of the cell 

 contents of the different groups, and the changes they 

 undergo during the process of division. 



» From the 'Journal of Botany,' July, 1872. 



