12 METHODS. 
passed into absolute alcohol, in which magenta or another aniline dye soluble 
in alcohol is dissolved. In this solution the sections very rapidly become well 
stained. They are not washed after this, but immediately transferred into 
xylol, in which the magenta, azur, etc., are insoluble, and then mounted in 
balsam. By this method the canals and the flagellate chambers can be made 
out in many a perfectly hopeless looking specimen. 
2. THE SKELETON. 
For the study of the arrangement of the spicules, and of the skeleton in 
general, thick radial sections made in the manner described above, but not 
stained, gave the best results. Such sections even of hard forms with a con- 
tinuous skeleton-net, like the Euretidae, can be cut without difficulty. 
3. THE SPICULES. 
My method of fractional sedimentation with final centrifugation has 
also been employed in the examination of the Hexactinellida. On account of 
the great amount of foreign siliceous material (skeletons of Radiolaria, etc.) 
in many of the specimens these spicule-preparations are, however, often not 
so clean as one would wish. To obtain clean preparations of the larger spicules 
I made a heap of spicules of sediment (I) by boiling a piece of the sponge in nitric 
acid, allowing it to settle a short time and drying in the usual manner. From 
this I, or rather my wife, who in time grew exceedingly expert, picked out under 
the microscope the spicules wanted. A fine needle, the point of which was 
rendered sticky with Schellibaum’s mixture of collodion and clove-oil, was used 
in this work. These spicules were then regularly arranged on a slide, also 
covered with a thin layer of Schellibaum’s mixture. To this they adhere, and 
can be immersed in balsam and covered with a cover-glass without becoming 
disarranged. 
The preparations of the smaller spicules of sediment (II), etc., and the cen- 
trifugated ones were heated till all the chloroform used for dissolving the balsam 
had evaporated and only the previously boiled balsam, which is quite hard at 
ordinary temperatures, was left. They were then, whilst cooling, pressed between 
the leaves of a book. In this way preparations are obtained which are much 
clearer than unpressed ones, and which can be examined with the highest powers 
much more conveniently. 
