26 



Marine Invertebrates 



H, f= 



G 



the other jars. As soon as the lowest level is reached (determined by the 

 position of the short arm of the siphon) the system begins to fill up 

 and the level in all the jars rises. The rate of flow of water may be 

 regulated to obtain the desired tidal interval. This arrangement was 

 first employed by H. F. Prytherch in a study of the effect of oil pollution 

 on oysters (Galtsoff, Prytherch, et al., 1935). (See note 2 on p. 50.) 



Circulation of water in a closed system. Many organisms may be 

 maintained in a limited supply of seawater if the latter is kept in circu- 

 lation and is systematically filtered. Various simple devices designed 



to meet these requirements are based on 

 the use of an air pump. The following 

 is the description of a simple but efficient 

 device (Fig. 31) designed by Burch and 

 Eakin which we copy from Science 

 (1934). The pump (P) (Fig. 31) is 

 made from a pyrex glass test-tube, 10 cm. 

 high and 1.5 cm. in diameter. A glass 

 tube (A) 5 mm. in diameter is sealed to 

 the side of the test-tube approximately 2 

 cm. from the mouth and then bent 

 parallel with the test-tube. A similar 

 glass (B) is sealed to the base of the 

 test-tube. The pump is placed in an 

 inverted position in the reservoir and an 

 exceedingly small air current is permitted 

 to enter the pump through the glass tube 

 (A) at the side. The exact depth at 

 which the pump will give a maximum 

 efficiency may be determined by experi- 

 mentation; however, the pump should be 

 at least 15 cm. below the water level in the reservoir. (See note on p. 50.) 

 Another method developed by Cleve (quoted from Hagmeier, 1933) is 

 shown in figure 32. The bottom of a tank is covered with a thick layer 

 of sand (sd) through which water is sucked into a funnel (F) forming 

 the lower end of the siphon, and is emptied into a small tank filled with 

 sand and charcoal (ch). From a filter tank by a similar arrangement of 

 siphon and funnel (Fi) the water enters into a U-shaped glass tube (U). 

 Bubbles of air, blown in at point L gradually push the water into the 

 horizontal tube (T) and back into the tank. By using this arrangement 

 various marine forms may be kept for a very long time in a small amount 

 of seawater. 



A similar arrangement for aeration and circulation of water was used 

 by Browne (1907) for the cultivation of hydroids (Fig. ^t,). Air blown 



Fig. 31. — A device for water 

 circulation. After Burch and 

 Eakin. P, pump; A, B, glass 

 tubes. 



