The Relations between Marine Animai and Vegetable Life. 391 



are od an average respectively .470 aud .774 mgm.: by the erabs 

 .801 and .698 mgm., by the molluscs .069 and .055 mgm., and by 

 the holothui-ians .051 and .026 mgm. Thus the favourable effect 

 produeed on the size of the larvie seems to bave been more or less 

 proportionate to the degree of contamination of the water. This is 

 especially borne out by the tvvo experiments with fish, in one of 

 which both the relative increase in the size of the larvse and the 

 amount of fouling of the water were so very much larger than in 

 the other. Doubtless there is a limit to the favourable effect of the 

 products of animai excretion on larvai growth, but apparently it was 

 not reached in any of the above experiments. With regard to the 

 three remaining experiments, in which a negative effect was produeed, 

 the influence does not seem proportional to the amount of fouling, 

 but the data are obviously insufficient to decide the question either 

 one way or the other. 



These values for the relative amounts of ammonia added to the 

 water bave an interest quite apart from their relation to larvai growth. 

 Thus they give one an idea as to which of the animals commonly 

 kept in marine aquaria exert the most contaminating influence on 

 the circulatiug water. These data give no absolute estimate of this 

 influence, but they are quite sufficient to indicate that fish and crabs 

 act very much more harmfully than molluscs and holothurians. 

 Anemones and medusse apparently occupy a more or less intermediate 

 Position, but the fouling efifects of the latter animals, considering the 

 large proi)ortion of water in their tissues, is in reality quite considerable. 



If an attempt be made to explain these remarkable effects of 

 contaminated water on larvai growth, attention should first be directed 

 to some observations cited in the previously mentioned papera In 

 this it was shown that the addition of one part of urie acid in 70,400 

 to the water caused an increase of \1.1% in the size of the larvse, 

 and that it was only when the amount added was increased to one 

 part in 28,000 that an adverse effect was produeed. Similarly also 

 the addition of urea to the water increased the size of the larvse 

 by about 2.7^, and the addition of even considerable quantities of 

 carbonio acid gas also caused a very slight increase. No explanation 

 of these unexpected results was arrived at, but it was suggested that 

 the ideas hitherto entertained as to the adverse effects of products 

 of metabolism on the growth of tissues might be mistaken ones, and 



1 ibid. pag. 595—598. 



26* 



