142 Phylum Coelenterata 



ously.* Some other cladocerans such as Simocephalus are easily cul- 

 tivated also but are too strong and powerful for the hydras or else tend 

 to stay on the bottom out of reach. Hydras will not eat ostracods. Oli- 

 gochaete worms are eagerly accepted but their habits are such that 

 the hydras would seldom have a chance to catch them. The very tiny 

 newly hatched Daphnia in a Daphnia culture may be used as food for 

 Chlorohydra viridissima; some small forms such as Ceriodaphnia or the 

 bosminids are suitable and may be grown like Daphnia. [See pp. 207- 

 220.] In case of necessity hydras may be fed on oligochaetes such as 

 naids, tubificids, or enchytraeids, and often these may be purchased from 

 pet shops. It is necessary to cut these up into pieces and to place the 

 pieces in contact with the tentacles with a dropper or forceps ; otherwise 

 they fall to the bottom where they are out of reach of the hydras. This 

 method of feeding is very time-consuming, but may be used when it is 

 desired to save valuable experimental material. Experimental material 

 which does not feed well of its own initiative, may often be fed success- 

 fully by placing a crushed daphnid, Cyclops, or bit of oligochaete in con- 

 tact with the tentacles. 



Tubificids are easily maintained in the laboratory for food by placing 

 them in containers having two or three inches of pond mud on the 

 bottom. For food, almost any kind of organic material such as boiled 

 lettuce leaves, boiled wheat grains, pieces of bread, or bits of animal 

 flesh, may be added from time to time. 



THE CULTURE OF SOME MISCELLANEOUS SMALL 



INVERTEBRATES 



Paul Brandwein, Washington Square College, New York University 

 Hydra. These animals are maintained in great numbers in balanced 

 aquaria when they are fed constantly with any of the Entomostraca men- 

 tioned below. 



Plathelminthes. Stenostomum may be cultured using the method used 

 for Paramecium. [See p. 63.] Planaria are usually cultured in enameled 

 pans containing clear pond or spring water; they are fed with boiled 

 egg yolk or fresh liver, care being taken to remove the excess food at 

 the end of a few hours before putrefaction occurs. The Planaria are cut 

 transversely when they reach the size of about 8-12 mm. with a 00 

 cover glass; regeneration occurred rapidly.** 



* Editor's Note: William LeRay and Norma Ford, of the University of Toronto, call 

 attention to the fact that in contrast to the grey hydra (H. vulgaris americana) the brown 

 species (Hydra i = Pelmatohydra] oligactis) stings its prey only when it needs it for food. 

 Thus in a culture of the brown form the uneaten Daphnia continue to live. The grey 

 hydra on the other hand stings to death any Daphnia which it happens to touch and on the 

 bottom of its culture bowl there will be found a ring of the dead crustaceans. M.E.D. 



** This method for Planaria does not differ significantly from the procedure recommended 

 by the commercial houses which supply this organism. 



