1026 The American Naturalist. [November, 
MICROSCOPY. 
. Methods of Preparing Molluscan Ova.’—The results of my 
work for the first three months wore. not promising. and it was not until I 
had hit upon m reparıng surface views of the entire 
ova that any detailed study of the cleavage could be made. Since I 
owe most of my results to this method and since I am convinced that 
it may be profitably employed in the preparation of the surface views 
of many different objects I believe it merits a detailed description. 
The ova were fixed in many different fluids—Kleinenberg’s Picro- 
sulphuric, Picric acid in sea water, Merkel’s, Perenyi’s, Flemming, 
stronger and weaker, Auerbach’s, Corrosive sublimate, Chromo-formic, 
Chromo-acetic and absolute aleohol—but none of these methods for a 
moment compare with the first named, i. e. Kleinenberg’s stronger 
picro-sulphuric. Theova were left in this for a length of time vary- 
ing from fifteen minutes to one hour and were then gradually trans- 
ferred to 70% alcohol. They were left in this until all traces of picric 
acid had been washed out and were finally preserved in 95% alcohol. 
During the first year of the work many of the preparations were ruined 
by becoming very dark, owing I think to the extraction of tannin from 
the corks. This trouble was afterward avoided by using rubber corks, 
or better still by coating ordinary corks with a thin layer of paraffin. 
As a result of many experiments with almost every one of the com- 
mon staining fluids, I found that the best method of preparing surface 
views of the whole egg or embryo was the following:—(1) Transfer 
the object gradually from alcohol to water. (2) Stain from five to ten 
minutes in a solution of Delafield's (Grenacher’s) Hematoxylin diluted 
about six times with distilled water and rendered slightly acid by a 
trace of HCl. (3) Dehydrate and clear in oil of cedar or cloves. 
(4) Mount in Balsam supporting the cover glass so as to prevent 
crushing. By occasionally softening the balsam with a drop or two of 
xylol and slightly moving the cover glass the objects can be rolled into 
any position desired. 
By this method wonderfully beautiful surface preparations were 
obtained showing with remarkable clearness not only the nuclei and 
cell boundaries but also the caryokinetic figures and in many cases the 
archoplasmic spheres and centrosomes. One very considerable advan- 
!Edited by C. O. Whitman, Chicago University. 
(Extracted from a paper to be published later on the development.) 
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