WITH THE MICROSCOPE. 153 



tube used as a syphon, and the bottom covered with well-washed 

 shingle. The tank may then be filled up with sea water, or artificial 

 sea water may be made with Tidman's sea salt in the proportion of 

 about one pound to three gallons of water, the exact proportions 

 being determined by aid of a hydrometer, which should stand at 

 i '026. Should the water be too salt the stem will rise till perhaps 

 i "030 of the scale appears above the level of the water, in which 

 case more common water must be slowly stirred in. If on the 

 other hand there is not sufficient salt, the stem will sink towards 

 i '020 and more salt must be added till the hydrometer registers the 

 proper specific gravity of natural sea water. As evaporation causes 

 the water to become concentrated, it should from time to time be 

 tested with the hydrometer and the necessary amount of water 

 added. The next step is to get the rockwork covered with the spores 

 of seaweeds, by placing several small healthy tufts of Ulva, or 

 Enteromorpha in various parts of the tank where they are fully 

 exposed to light, In a short time minute vegetable growths will 

 make their appearance all over the tank. The growth on the front 

 glass must be removed as fast as it is formed by a sponge tied to a 

 stick. After this growth has appeared the tufts of weed may be 

 removed. The amount of light admitted to the tank must now be 

 carefully attended to, so as just to cause the evolution of bubbles of 

 oxygen, without stimulating the vegetable to an over-abundant 

 growth which would cloud the water. Animals may next be intro- 

 duced slowly and not in too great numbers, the lowest in organisa- 

 tion first, the higher forms when the tank is evidently working well, 

 and the first things introduced appear healthy, and the water is clear 

 and sparkling. It is well occasionally, if not daily, to remove a 

 portion of the water into a glass vessel and allow it to return to the 

 tank through a fine jet, by which means the water is broken up into 

 spray as it returns to the tank. There are various ways of effecting 

 this important process of aeration of the water. 



In the Athenaeum for March loth, 1860, Mr. Highley described 

 a very convenient aquarium arrangement well suited for a microscopist 

 who is making a temporary visit to the coast, which I here extract. 



" I may mention a plan I have employed with great success when 

 making temporary visits to the coast, which will be found very con- 

 venient to those who wish to classify the animal forms obtained for 

 observation. I take a nest of German beakers (without spouts) and 

 pack them in a zinc case : on my arrival, I fill them with fresh sea 

 water, and place them in a sunny window ; I then collect a number of 

 limpets on whose shells enteromorpha and ulva are growing. These 

 will be found to be small but vigorous plants. I remove the animals from 



