CULTUKE OF PLANKTON DIATOM THALASSIOSIRA GRAVIDA CLEVE. 429 



siosira, as described in the experiment Avith ulva infusion. No growth 

 was obtained in the flask. 



Ulva Ash. A piece of ulva measuring about 5 cm. by 3 cm. was 

 washed in several changes of double-distilled water. It was then put in a 

 porcelain crucible, dried and heated over a bunsen burner till it was 

 reduced to a white ash. The ash was added to a flask containing 75 c.c. 

 of artificial miqueled sea- water, w^hich was boiled, allowed to cool and 

 inoculated with Thalassiosira, as in the two previous experiments. The 

 result of the experiment was again negative. 



Experiments with Hemimysis. In order to test whether the products 

 of animal metabolism could immediately supply the substance sought 

 for, the following experiment was carried out with Hemimysis lamornoe 

 Couch, a small crustacean which lives in numbers in the Laboratory 

 tanks. In the first experiment (Exp. 404) four Hemimysis w^ere passed 

 through two changes of Berkefeld filtered water, the animals being placed 

 on a piece of filter paper to remove surplus fluid before being placed in 

 each change of water. They were then passed in a similar way through 

 two changes of artificial miqueled sea- water (75 c.c. was used altogether, 

 being divided into two portions), and finally placed in a fresh quantity of 

 the artificial miqueled sea-water (75 c.c). They remained healthy and 

 active and deposited a considerable amount of faeces on the bottom of 

 the vessel. After they had been in the water four hours the Hemimysis 

 were taken out and the w^ater placed in a culture flask and brought to 

 the boil. A control experiment with 75 c.c. artificial miqueled sea-water 

 to which 3 c.c. of tank water had been added was set up and brought to 

 the boil in the same way. On the following day both flasks were in- 

 oculated with two drops of a Thalassiosira culture. During the first 

 week there was a very small growth of diatoms in the flask with the water 

 in which the Hemimysis had been, which died out during the next few 

 days. This growth was similar to that which usually occurs in artificial 

 miqueled water to which nothing has been added. The control experiment 

 to which 3 c.c. tank water had been added gave a very fine growth from 

 the first, which persisted for at least five months. The result of this 

 experiment was therefore negative. In another experiment, carried out 

 in other respects in practically the same way, the Hemimysis were 

 allowed to remain living in the water for twenty-four hours before 

 they were removed. The result was again negative. 



In a third experiment five Hemimysis lived for nineteen hours in 75 c.c. 

 artificial miqueled sea-water to which 3 c.c. of tank water had been added. 

 The animals were removed, the water boiled, and when cold inoculated as 



