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 inixture of collodion and clove-oil, was used 

 in tills 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 inunersed 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. 



