The Relations between Marine Animai and Vegetable Life. 347 



In this instance we see that the exposure to direct siiulight liad 

 by no raeaus a favourable effect on the action of the alga, as the 

 free amraonia was diminished much more slowly, and the organic 

 ammonia increa sed much more (juickly in amount than before. lin- 

 fa vourable results in experiments of this kind cannot, however, be 

 considered of much importance, as they may be due merely to the 

 alga undergoing au abnormal decomposition, due to the artifìcial 

 conditions. Thus in the present case, the Uloa was to a large extent 

 bleached by the action of the sunlight. 



Judging from the rapidly purifying effect of Ulva upon the free 

 ammonia present in the water, one might expect that water thus 

 treated would bave a beneficiai effect upon animai lite, as evidenced 

 by the growth of Echinoid larvse. Such seems to be actually the 

 case, if precisely the best conditions as to the amount of Ulva used, 

 and the time it has been allowed to act, bo observed. Thus larvso 

 grown in a sample of the above mentioned water, after treatment 

 with Ulva for four days, were found to be 14.4^ larger than those 

 grown in normal tank water (vide Exp. 50). Also larvse grown in 

 the water exposed to the action of Ulva in direct sunlight for four 

 days, were 16.8X larger than the normal (Exp. 39). As will be 

 shown later on however, this favourable effect must bave been largely 

 due to the direct effect of the sunlight on the water. In another 

 experiment. No. 9, larvae were allowed to grow in a specimen of 

 water in which other larvse, together with some Ulva, had previously 

 been growing for ten days. They were found to be practically un- 

 altered in size, they being .06^ smaller. On the other band in a 

 parallel experiment. No. 10, in which larvse were grown in a specimen 

 of water in which other larvaj had been allowed to develop without 

 the addition of Ulva, the size was diminished by 6.8^. In both 

 these instances the originai larvse were of course filtered off from 

 the water before the fresh fertilised ova were introduced. 



A negative effect is, however, produced in some cases. Thus in 

 Exp. 93, in which the water was exposed to the action of 12 sq.cm. 

 of Ulva per litre for four days, whereby the free ammooia present 

 was diminished by 46^, and the organic ammonia increased by 8^, 

 the larvse were diminished 1.0^ in size. 



