22 



Marine Invertebrates 



Qj) 



Fig. 



>6. — The overflow 

 siphon. 



(D). A bucket (F) with an automatic siphon (S) is suspended from 

 the other end of the lever. The bucket is filled with water delivered 

 through a flexible hose (H). The size of the bucket is so adjusted that 

 when it is almost full it swings down and pulls the plate (A). As soon 

 as the level in the bucket is slightly above the upper level of the siphon 

 the water is emptied through it and the glass plate swings down pulling 

 up the bucket. A bar (E) stops the downward motion of the bucket 



whereas a piece of string (K) prevents the 

 striking of the glass plate (A) against the 

 bottom of the tank. The tank may be kept 

 under a cover with a small hole permitting the 

 passage of a glass rod (B). A plunger may 

 be made of celluloid as well as of glass. The 

 instrument is easy to make according to de- 

 sired specifications. If several jars are used, 

 one master bucket may operate all the plungers 

 which are connected to the lever by means of 

 a series of strings and pulleys. Plunger jars are very successfully used 

 in the Plymouth laboratory in maintaining and rearing very delicate 

 marine animals. 



Constant level arrangements. The simplest way to maintain a con- 

 stant level of water in a tank is by inserting a horizontal pipe at the de- 

 sired height in the wall. The opening of the outlet must be covered with 

 a screen to prevent the escape of the animals. This arrangement may, 

 however, prove unsatisfactory in many cases because of the clogging of 

 the screen. Better results are obtained with a vertical overflow pipe 

 passing through the bottom of a tank and protected with a metal screen 

 cylinder extending above the level of the water. 

 The cylinder is mounted on a tightly fitted cork or 

 rubber stopper with a hole for the passage of a 

 tube. The size of the mesh, of course, depends 

 upon the dimensions of the organisms kept in the 

 tank. The metal screen used for this purpose 

 should not be corrosive in seawater. According to 

 Richards (1933) screens made of pure nickel or 

 of stainless steel are the least toxic. 



The desired level of running water may be 

 maintained by using an overflow siphon which is 

 made by bending over one arm of a U-shaped glass 

 and placing it in a position shown in figure 26. 

 The controlling level of the siphon may be 

 changed easily by attaching a rubber tubing to the short arm and fasten 

 ing the free end of it at the desired height. 



3 



Fig. 27. — The overflow 

 siphon. Adapted from 

 Hagmeier. 



