24 



Marine Invertebrates 



A few organisms may swim back through the siphon connecting the 

 second and the first jar and be lost. The opening of the controlling 

 siphon may be covered with plankton silk or other fine material to pre- 

 vent the escape of minute organisms. This arrangement has been suc- 

 cessfully used by the author in rearing and maintaining small crusta- 

 ceans, the larvae of mollusks and echinoderms, and small jelly fishes. 



Further improvement of this method was made by F. G. Walton 

 Smith whose personal communication reads as follows: "Rapid clog- 

 ging of the pores of this material (bolting silk) is prevented by dipping 

 the mouth of the siphon under the surface of molten paraffin wax melt- 

 ing at 48 ° C. and then blowing air through the other end as it is removed. 

 The resulting smooth coating of wax on the fibers seems to prevent 



Fig. 29. — The current rotor. 



the entanglement of larvae and allows the filter to work efficiently for 

 a much longer period than would otherwise be the case. The net is 

 attached to the siphon by means of a wide rubber band, and is of such 

 a nature that when worked, the openings are just small enough to serve 

 to retain the larvae." Using this technique Dr. Smith had no difficulty 

 in growing oyster larvae at the U. S. Bureau of Fisheries Station at 

 Beaufort, N. C. 



Slow exchange of water may be obtained by using the so-called "filtros" 

 block which may be installed as a partition in the aquarium, or by 

 inserting a Berkefeld filter and slowly sucking the water through it. 

 Stone filters become clogged very quickly and require frequent changes. 



Current rotor. This instrument is designed to change the water in 

 the aquarium without losing the small organisms living in it. The es- 

 sential feature of the apparatus (Fig. 29) designed by Galtsoff and Cable 

 ( 1933) is a cylinder (A) of 60 mesh or finer nickel screen suspended in a 

 tank and rotated by means of an electric motor. Rotation of the 

 cylinder when placed at one end of an oblong aquarium sets up a com- 

 plex system of currents the direction of which is indicated in the accom- 



