ON MOUNTING. 157 



desired results "have been obtained by Dr. Yan 

 Heurck, who succeeded in providing an admirable 

 substitute for balsam in gum-styrax. It will pro- 

 bably be found that diatoms mounted in gum-styrax 

 are less liable to accidents than balsam " mounts," 

 as the latter becomes resinous in time, and the 

 covers are liable to " spring," the result of which 

 is the appearance of prismatic colours in the balsam, 

 which are not only a great eyesore, but sadly 

 deteriorate the slide. Grum-styrax, the method of 

 preparing which for use has been described at page 

 105, may be considered absolutely permanent and 

 unalterable. The solution is used in the same 

 manner as Canada balsam. Styrax solution is even 

 easier to work with than balsam, and air-bubbles 

 are not produced in it by the application of heat. 

 Monobromide of naphthaline as a medium in which 

 to mount diatoms, and the method of its application, 

 have been described at page 105. 



Cleaning and Mounting Polycystina and 

 Radiolaria. 



The siliceous shells of these lovely organisms, 

 the beauty of which is only equalled by their variety, 

 are found in profusion, and intermixed with diatom- 

 aceous valves, often of extreme beauty and rarity, 

 in the deposits (or so-called " earths ") of Barbados, 

 the Bermudas and the Nicobar Islands, whilst an 

 entirely new and magnificent deposit was discovered 

 by the late Captain Perry, of Liverpool, at Jeremie, 

 Haiti, which contains not only a large number of 

 novel species of polycystina, but many entirely new 

 varieties of diatoms. The celebrated " Challenger " 



