MICROSCOPIC PREPARATIONS IN MARINE ZOOLOGY 333 



object is pressed by the cover, not only will you have no 

 end of trouble, but the parts will be distorted. 



Whole objects may be mounted with very good results 

 in glycerine jelly. These do not show fairly as transparent 

 mounts, -but give splendid and lifelike results for illumina- 

 tion by the spot lens or paraboloid, which accessory to the 

 microscope shows the object brilliantly illuminated on a 

 background of black. 



Mounting in this way is simple. Place the objects for 

 a little while (either from water, or from the spirit in 

 which they were preserved) in somewhat dilute glycerine. 

 Place the bottle of glycerine jelly in a pot of hot water 

 until the contents are quite fluid ; warm the sunk-cell 

 slip, and with a glass rod fill the cavity. Place the object 

 symmetrically in place, warm a cover glass, press it down 

 in the usual way, and put clips to the cover edges. In a 

 few hours the jelly will be set. Wash off the exuded portion 

 with cold water and a little brush a soft tooth-brush is ex- 

 cellent. Place on the turn table, and give a good strong ring 

 of the brown cement, or of japanner's gold size, or of any 

 substance that runs well and is not soluble in water. Finish 

 in black. 



This is not a complete exposition of microscopic tech- 

 nique, but it embodies every point that is required for 

 the marine zoologist. 



There may be various exigencies now and again to be 

 met, but none that ordinary intelligence will not be able 

 to cope with. 



One little point, however, that still requires mention, or 

 a difficulty may present itself. 



When an entire object, say a young shrimp, is taken 

 from the absolute alcohol and placed in the oil of cloves to 

 clear it will float, and the alcohol, evaporating at a greater 

 rate than the clove oil penetrates, may admit air into its 

 interstices, and spoil it entirely. To obviate this, either 



