28 



But the tanks being rectangular it was found that the larvae drifted 

 out of the current and settled in the corners, and further the current 

 was not strong enough to keep the larvae from the bottom of the 

 tank when they showed a tendency to remain there. It was, as 

 a rule, some five or six days after hatching before any number of 

 the larvae was observed on the bottom, and after that the number 

 varied somewhat, being greatest at the periods of moulting. 



To some extent this settling of the larvae, which allowed of 

 the less active being attacked by the more vigorous and stronger 

 swimmers, was prevented by stirring the water frequently durmg 

 the day mth a wooden paddle. This not only moved the larvae 

 but also any food which had fallen to the bottom of the tank. 



The constant supply of water to the tanks brought a quantity 

 of mud and fine sand, the amount varying according to the condition 

 of the sea. When the sea was other than calm it was impossible 

 to allow time for the water to remain long enough in the supply 

 tanks to settle, and it was found that the bottom of the rearing 

 tanks became covered with fine sediment which had to be removed, 

 periodically. Experiments 7 to 11, in which the water was aerated 

 by air driven through pieces of rubber tubing punctured by a needle, 

 were therefore conducted, and the water supply was regulated 

 to allow of only clear water being used. Two tubes connected, 

 with the air supply, were led into each tank, and the pieces of 

 punctured rubber tubing, about three inches in length, were kept 

 down by means of small stones. When suitably arranged these 

 gave a current, but it was weak and of httle or no value, and here, 

 as before, the water was frequently moved by a wooden paddle. 



The foods used were such as could be most easily obtained 

 in quantity, and consisted of shore crab {Carcinus maenas), mussel 

 and fish (whiting). Later, fish fiver and ox fiver were tried. The 

 food was put through a mincer and then aerated by driving water 

 from a fine nozzle through a piece of tubing into the dish containing 

 the food By this method it was possible to cause the greater 

 part of the food, except in the case of ox fiver, to float or be 

 suspended in the water for some hours. Food was given daily, 

 after first removing the surplus from the previous dsij. AU the 

 foods used were taken by the larvae and carried about by them 

 until apparently sufficient had been eaten. 



