The Relations between Marine Animai and Vegetable Life. 399 



in Expts. 16 and 17, Strotigylocentrotuti larvse grown in Strongijlo- 

 centrotus-iovX^^ water were diminished by 2.3^, but grown in 

 Sphcerechinus-i^wX^^ water, by 1.%%. On the other band Ecìiinua 

 larvas in Stro7igylocentrotus-io\x\Qà. water failed to reach the full 

 larvai stage at ali. Taken as a whole therefore these results cannot 

 be held to decide defìnitely in either one direction or the other. As 

 they were so variable, and so troublesome to carry out, they were 

 not continued any further. The nurabers representing the percentages 

 of ova reaching larvai development also fail to point either one way 

 or the other, they being roughly inversely proportional to the diniinu- 

 tion effected in the size of the larvse. 



On the right side of the table are given the absolute amounts 

 of ammonia in the fouled water, and also the excess of this ammonia 

 over that present in the water in which the normal larvie were 

 grown. It ueed scarcely be said that wheu Echinus larva; were grown 

 in the fouled water, other Echimis larva;, to serve as the standard 

 of coniparison, were at the sanie tinie grown in normal tank water. 

 On an average, the composition of the water, as far as the ammonia 

 is concerned, is about the sanie as that present in the previous ex- 

 periments on the fouling eftects of various animals; but, as might 

 be expected, it is not nearly so variable. It obviously depends closely 

 upon the number of larvie which had been developing in the water, 

 and the number of days of development. 



The Effects of Certain Salts on Larvai Growth. 



We have seen that thus far no definite due has been obtained 

 as to the nature of the particular products of excretion which may 

 cause either a positive or a negative effect on larvai growth. They 

 were shoWn not to be simple organic bodies as urea and urie acid. 

 Is it possible that they may bè of an even simjiler nature, such as 

 ammonia itself, or some of its derivatives as the amines and 

 amido bodies? Wìth reference to these latter bodies, no observations 

 were made, but the results obtained with the simple salt, am- 

 monium chloride, tend to show that ammonia derivatives may 

 be a very important factor in the question, These results were as 

 follo w: 



