20 Transactions of the Society. 



E, having a like cut through it for the passage of an outlet thread 



F, is cemented at the same distance from the opposite end of the 

 slide. In this condition the slide being filled with water to the level 

 of G-, any current coming in through the intake thread D would 

 pass directly across the top of the water in the cell, and pass out 

 by the outlet thread F, and organisms near the bottom of the cell 

 would not be benefited by a change of water ; I therefore cement 

 a very narrow slip H of the same covering glass as before to the 

 inner side of the outlet end of the cell, commencing at the top of 

 the slide, and extending to very nearly the bottom, so as to leave 

 about yV i^ch between E and H. If the intake thread is connected 

 with a bottle of water placed above the level of the slide, water 

 entering by the intake thread will pass in a diagonal direction 

 from D to the left and bottom of the cell, where the influence of 

 the suction set up by the siphon-like action of the outlet thread 

 makes itself felt, and there is a regular current in the direction 

 ol" the arrows. 



The front of the cell is formed of a piece of thin covenng glass 

 of li inch by |, and two small square blocks of glass I, cemented on 

 each side, will hold this covering glass sufficiently firm to prevent 

 it sliding on the organism and crushing it. 



Such a growing slide will hold about 1 drachm of water, and 

 taking the rate of the drops from the outlet thread as about one 

 per minute, the whole of the water in the cell is changed once in 

 an hour, while at the same time the current is not sufficiently 

 strong to carry away more than the finest and Hghtest bodies. •_ It 

 allows of fair observation with a ^-inch objective, and if desired 

 could be made with thinner glass, so that a ^-inch or |-inch might 

 be used. 



