1891.] MICEOSCOPICAL JOURNAL. 87 



inch by r inch), having a narrow ledge of glass (about ^ inch wide 

 and extending nearly its whole length) cemented to its lower border 

 with marine glue ; to this is cemented at right angles a strip of thin 

 covering glass about ^ inch wide and about i^ inch from the end of 

 the slide, having a narrow channel cut through it for the passage of an 

 intake thread. A similar strip having a like cut through it for the pas- 

 sage of an outlet thread is cemented at the same distance from the 

 opposite end of the slide. In this condition, the slide being filled with 

 water any current coming in through the intake thread would pass 

 directly across the top of the v\^ater in the cell and pass out by the out- 

 let thread, and organisms near the bottom of the cell would not be 

 benefited by a change of water; therefore, cement a very narrow strip 

 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 j\ inch between. 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 direc- 

 tion to the left and bottom of the cell, where the influence of the 

 suction set up by the syphon-like action of the outlet thread makes 

 itself felt, and there is a regular current. 



The front of the cell is formed of a piece of covering-glass of i^-inch 

 by ^, and two small square blocks of glass, cemented on each side, will 

 hold the covering-glass sufliiciently firm to prevent it sliding on the or- 

 ganism and crushing it. 



Such a growing slide will hold about one drachm of water, and, tak- 

 ing the rate of the drops from the outlet thread as about one per min- 

 ute, 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 lightest bodies. It allows a fair obser- 

 vation with a ^-inch objective, and, if desired, could be made with 

 thinner glass, so that a -jl-inch or ^-inch might be employed. 



In using this growing slide any reservoir of water placed slightly 

 above the level of the stage will answer the purpose of supply ; but the 

 author has had a support fixed to the movable stage of his microscope 

 which carries a small bottle of water at a suitable height, and thus the 

 water supply and the growing slide are made to move simultaneously 

 without any disturbance of the object during its examination ; in this 

 manner he was enabled to carry on continuously for two months the 

 observation of the development of Corethra pluinicornis^ when the 

 successive changes in its organization were carefully noted and drawn. 



Delineation of Objects. — Drawings from microscopical observa- 

 tion are made by means of an optical arrangement placed over the eye- 

 piece of the microscope, and called a camera lucida. There are man}' 

 forms of this instrument, but the principle is the same. The rays of 

 light from the object are reflected at an angle, and the object made to 

 appear as if projected on the drawing paper, when its outline and de- 

 tail can be drawn with a pencil. Some are made to be used when the 

 microscope is in a vertical position, which is most convenient for the 

 examination and drawing of infusorial life. But if confined in a shal- 

 low trough the microscope may be placed horizontally, and a camera 

 lucida made upon the following principle may be used : The cap of the 

 eye-piece being removed, a collar of brass may be substituted, carrying 



