348 



M. Vernon 



In the experiments thiis far described, the larvae were allowed 

 to grow in water previoiisly exposed to the action of the alga. 

 Another series was made, in which pieces of Ulva were added to 

 the water in which the fertilised ova were developing, and in which 

 therefore the larvie were in direct relation to the alga throughout 

 their growth. The resiilts obtained are given in the table. 



Here it will be seen that only in one case, Exp. 43, were the 

 larvjc increased in size. In two others they were only very slightly 

 affected, but in the other three distinctly reduced in size. With the 

 exception of Exp. 24, the alga seems to have exerted a more and 

 more unfavonrable effect in proportion to the amount present in the 

 water. Presumably in all experiments but the first in the table, the 

 amount of Ulva used was too large. In the last two columns of the 

 table are given the percentage differences in the amounts of free 

 and organic ammonia in the water after eight days growth of the 

 larvse, as compared with the amounts present in parallel series of 

 experiments, in which the larvje were allowed to grow without the 

 addition of any Ulva. From these figures it will be seen that in 

 every case the amount of free ammonia was considerably reduced, 

 this reduction being more or less proportionate to the amount of 

 Ulva present. In four out of the fi ve observations made the organic 

 ammonia was also reduced considerably in amount. Contrary to the 

 result previously obtained, it must be concluded therefore, that when 

 the amount of organic ammonia present is fairly large, as is the 

 case when larva? are growing in the water, the alga has the power 

 of partially removing it. In the light of these ammonia determinations, 

 it seems ali the more curious that the larvje should have been as a 

 rule diminished in size. It is possible however that the mere size 



