558 L. R. CKAWSHAY. 



Water. 



(A) Tank Water.— Water circulated through the tanks of the Labora- 

 tory from the supply stored in the reservoirs. This water is pumped up 

 into the reservoirs from the sea below the Laboratory at high water 

 spring tides. Li consequence of the large number of animals living in the 

 tanks it contains a considerable amount of excretory products. 



(B) Berkefeld Water. — Tank water treated with animal charcoal, and 

 filtered through a Berkefeld candle. In many experiments, owing to the 

 high salinity of the tank water, this w^as diluted with 5% distilled water. 



(C) " Outside " Water. — Water brought in from outside the Plymouth 

 Breakwater, and largely free from the contamination of the inshore 

 grounds. This was used sometimes untreated, sometimes sterilised, and 

 sometimes filtered through a Berkefeld candle. 



(D) Miquel Sea- Water. — Occasionally Berkefeld, usually " outside " 

 water, treated with the modified Miquel solution employed by Allen and 

 Nelson,* but chiefly used in considerably less strength, generally one- 

 third, in experiments here to be considered. 



Light. 



Additional illumination was obtained when necessary by placing sheets 

 of white paper or card, or of opal glass, under the vessels, and in 

 many cases behind them also. In some experiments the light was 

 partially or wholly cut ofi by screening the vessels with black paper. 



Food. 



In most of the experiments a culture of the Diatom NitzscJiia dosterium 

 was used as food for the animals. In some, the Alga Chlorodendron 

 subsalsum was used. 



Airrsupply. 



Artificial aeration of the water was employed at intervals in many of 

 the experiments for varying periods, and sometimes continuously, by 

 means of drawn-out glass tubes led into the vessels, and connected with 

 the general air-pressure system of the Laboratory. It may be said at once 

 that no definite advantage seemed to be gained by its use, assuming the 

 water to be naturally aerated at the outset. 



• Journ. Mar. Biol. Assoc, N.S., Vol. VIII., p. 428. 



