Opalina. 203 
well before covering to hold the slide, with the animals in cedar oil 
upon it, upside down for a few moments over the top of an ammo- 
nium hydrate bottle, and to do the same with the balsam on the 
cover-glass. My preparations so treated have not faded in ten 
months except near the edges of the cover-glass. Apparently the 
carbon dioxide of the atmosphere causes decolorization of the objects 
near the edge of the cover-glass. The objects can be kept from 
running out from the center toward the edge of the cover-glass by 
the simple but effective device of placing the balsam before covering 
in a complete circle just inside the outer edge of the cover. 
For sectioning single individuals in predetermined planes 
Yarsu’s (1904) Ulva leaf method was used. For imbedding large 
numbers of animals together I used either Boverr’s method of wrap- 
ping the animals in a bit of the sloughed skin of a large amphibian 
(Cryptobranchus), or a method which combines suggestions from 
LeFevre (1903) and from Pau Mayer (1907). In the latter method 
the animals are carried up to absolute alcohol in ordinary embryo 
glasses. After dehydration all but a few drops of the alcohol is 
drawn off. Then with a fine pipette the remaining alcohol, with 
the animals, is removed and placed in a small gelatine capsule 
(20 mm by 5 mm) which is set upright in a hole in a_pasteboard 
box (Text Fig. I, A). The ends of the box should be removed so that 
one can look through and see the objects in the bottom of the 
capsule. After the animals have settled to the bottom of the capsule, 
the supernatant alcohol is drawn off and xylol added. It is well 
to change the xylol once or twice to remove all trace of alcohol. 
After sufficient time, the xylol is removed, melted paraffin in added, 
and the capsule is set into the warm chamber. The paraffin must 
be changed to remove all xylol. With care this may be done with 
a warm pipette, but I find it much easier to effect the change in 
another way. After the animals have become well infiltrated with 
the paraffin, the capsule may be removed from its supporting box 
and its contained paraffin cooled by placing the capsule in cold 
water. After a few minutes the gelatine capsule will be softened 
and swollen by the water and the cylinder of paraffin can be easily 
removed. A second capsule should then be nearly filled with melted 
paraffin and the tip of the cooled paraffin cylinder, with the con- 
tained objects, be cut off and placed in the top of the capsule of 
melted paraffin and the capsule placed in the warm chamber. As 
the paraffin cylinder tip melts, the objects sink through the whole 
length of the capsule, losing en rowte whatever xylol they may 
