The Relations between Marine Animai and Vegetable Life. 395 



Strongylocentrotus ova grown in water tbiiled by Strongylocentrutus^ 

 on an average A^% developed, wbilst with fhe water fouled by 

 Splìcerechinus^ 61 % developed. Again in tbe experiments ou Sphcer- 

 echinus larvse, only a tbird as many of tbe ova developed in water 

 fouled by Sphcerechinus^ as in tbat fouled by Strongylocetitrotus. Stili 

 again, in the experiments with Echinus larvse, only 48^ of the ova 

 developed in water fouled by Echinus^ as against 1Ò% in tbat fouled 

 by Strongylocentrotus. 



Concerning the actual amount of fouling of the water by these 

 various species of sea-urchins, it is not possible to speak very de- 

 finitely, as in tbe first place, cbemical analyses were not made at 

 ali in several instances, and in tbe second place the analyses them- 

 selves were carried out after and not before tbe larvae had been 

 allowed to develop in the water, when of course many of the ex- 

 ereted products may bave been absorbed or changed by larvai or 

 bacterial growth. Tbat such a change did take place is almost 

 proved by the organic ammouia values. Thus in ali tbe six analyses 

 made, the organic ammonia was found to be either less than, or 

 practically the same as, tbat present in tbe normal unfouled water 

 after eight days' larvai growth. In the above series of experiments 

 with otber aninials, we saw on tbe otber band tbat the fouled water 

 always, with a single exception, contained very much more organic 

 ammouia than the unfouled. Also in the two experiments made with 

 sea-urchins (Nos. 46 and 48), in which the fouled water was analysed 

 before and not after larvai growth, tbe organic ammonia was 

 appreeiably increased. It would seem therefore tbat tbe larvse are 

 in some way or otber able to absorb or transmute the organic ammonia 

 introduced into the water by fouling. The free ammonia they do 

 not seem to bave much intluence upon, for the fouled water, after 

 larvai growth , contained as great an excess of it as was generally 

 present in the former experiments in which the fouled water was 

 analysed before tbe introduction of the larva?. 



What is the cbemical nature of these excretory products, which, 

 according to tbe species of tbe animai from which they are expelled, 

 will produce either a positive or a negative effect on larvai growth? 

 Doubtless comparatively simple nitrogenous bodies as urie acid and 

 urea bave a small intluence, but as has already been sbown, this 

 intluence is always a positive one. The major portion of the effect 

 must, one would think, be due to more complicated organic nitrogen 

 derivatives. It was thought tbat bodies such as the ptomaines migbt 



