408 THE MICROSCOPE. 



company with several aquatic plants, viz. Villisneria spi- 

 ralis, Anacharis alsinastrum, Pontederia crassipes, Papyrus 

 elegans, and Pistia stratiotes, which plants, by means of 

 their vital actions, as had long been well known, main- 

 tained the purity of the water, and, as in .the atmosphere, 

 kept up the balance between the animal and vegetable 

 respirations. Placed in the centre of my fern-house, and 

 nearly surrounded by rock-work (rising five or six feet 

 above the margin of the vessel), clothed with Adiantum 

 and other lovely ferns, and partially overshadowed with 

 the palmate leaves of Corypha australis, the plants and fish 

 continued to flourish for years. The only enemy I had to 

 contend with was a species of Vaucheria, which, from its 

 rapid growth, required to be kept constantly in check. 

 My friend, Mr. Bowerbank, always alive to scientific in- 

 quiries, followed up these experiments with equal success ; 

 but substituted sticklebacks and minnows for the gold- 

 fish, and a few snails, to get rid of the decaying leaves of 

 the plants." 



PRESERVATION OF THE POLYPIDOMS OF ZOOPHYTES. 



The following excellent and simple plan for preserving 

 zoophytes as wet preparations, so as to retain the polypes 

 and their tentacular arms in situ, was adopted by the late 

 Dr. Golding Bird. " For this purpose a lively specimen 

 should be chosen, and then plunged into cold pure water ; x 

 the polypes are killed almost immediately, and their ten- 

 tacles often do not retract : proper-sized specimens should 

 then be selected, and preserved in weak alcohol. Little 

 phials about two inches long should be procured, made 

 from thin flat glass tubes, so as to be half an inch wide, 

 and about a quarter of an inch, or even less, from back to 

 front. The specimens should be fixed to a thin platinum 

 wire, and then placed in one of these phials (previously 

 filled with weak spirits), so as to reach half-way down. 

 When several are thus arranged, they should be put on a 

 glass cylinder, and removed to the air-pump. On pump- 

 ing out the air, a copious ebullition of bubbles will take 



(1) A small quantity of gin thrown into distilled water answers the purpose 

 better than pure water, and specimens may be put up in the same. The animals 

 are nearly always preserved in their polypidoms by using this fluid to kill them. 



