OF THE 



133 



Fig. 31. ZOOPHYTE TROUGH. 



The Zoopliyte Trough. This little piece of apparatus 

 is almost indispensable to those who desire to watch the growth 

 and development of the larger animalcules and small aquatic 



plants. Several forms are in 

 common use, the most com- 

 plete being that shown in Fig. 

 31 . The trough itself is sim- 

 ply a glass tank, to which is 

 fitted a slip of thin plate glass 

 that acts as a division, and 

 enables the observer to keep 

 the objects close up to the 

 front plate. The distance of 

 the dividing plate from the 

 front plate is regulated by an 

 ivory wedge, and the dividing 



plate is kept firmly up to its place by means of a spring. This 

 contrivance enables us to regulate the thickness or width of the 

 tank, so that the interior of the vessel may be made so large 

 that it can be easily cleaned. 



A smaller and simpler form of the Zoophyte trough 

 is shown in Fig. 32. It consists of a simple glass box, 

 open at the top. The back 

 of the box is formed of a 

 stoutish piece of plate glass, 

 to which is cemented three 

 glass strips, forming the 

 bottom and ends. The front 

 is formed of glass as thin as 

 is compatible with durabil- 

 ity, and is also cemented to 

 the end pieces. The width 

 of the trough from front to 



back is generally from an eighth to a quarter of an inch. When 

 the trough is filled with water, and living animals are placed in 

 it, their changes and movements may be very readily watched. 

 Small troughs, such as that just described, are not difficult 

 to make, though the very low price at which they are sold (60 

 cents to $1.00) renders it scarcely worth the while of ordinary 



Fig. 32. ZOOPHYTE TROUGH. 



