390 H- M. Vernon 



Of the eleven experiments recorded in tbis table, we see that 

 in seven of tbem an increase in tbe size of tbe larvje was pro- 

 duced. Tbis increase varies in amouut from \A% to 8.3^, it being- 

 on an average AA%. Of tbe otber four experiments, one, No. 50, 

 does not properly belong to tbe present series of experiments, as tbe 

 eftect produced was due to an additional faetor, tbe introduetion of 

 seaweed into tbe water during larvai development. In tbe remaining 

 tbree experiments, tbe decrease in size is on an average only \A%. 

 Tbis most Gurions and unlooked for result beeomes even more 

 aecentuated by a study of tbe individuai experiments. These show 

 that it can be no mere chance wbether the water fouled by any 

 particular animai sball bave a favourable influence on larvai growtb 

 or not. As far as the observations go, it wonld seem a general rule 

 that tbe excretory products of lisb, crabs, moUuscs and bolothurians 

 bave a favourable influence on the growtb of larvae whilst those of 

 sea-anemones and medusa on tbe other band bave a sligbtly un- 

 favourable one. From tbe values calculated per unit volume of water, 

 we find that as an average of tbe two experiments made with fish, 

 tbe increase is l.'ò%. In the single experiment with crabs, tbe 

 increase is %\%: in tbe two with bolothurians it is \A%, and in 

 tbe two with moUuscs, \.1%. Of the tbree experiments in which 

 a negative effect was produced, a bermit crab with tbree auemones 

 attached to its shell was used in one case; otber anemones but 

 without any crab in the second; and a medusa in the tbird. The 

 average relative diminution in size is 1.1^. 



Upon the percentage number of fertilised ova reaching larvai 

 development, fouling of the water does not seem to produce a 

 favourable influence in the same way as it does upon the size, but 

 the effect is in any case ouly very sligbtly adverse. Tbus as a 

 mean of tbe eleven experiments, 63.7^ of tbe ova became full grown 

 plutei. Curiously enougb it would seem that in those experiments 

 in which there is a negative effect on tbe size of tbe larvse, there is a 

 positive one on the number, and vice-versa, but want of sufficient data 

 must preclude one from drawing any certain conclusion to tbis effect. 



In tbe last two columns of the table are given tbe relative 

 amounts of free and organic ammonia added to the water by tbe 

 fouling. These may probably be taken to give a fair criterion of 

 tbe relative capacities for fouling which the ditferent animals possess. 

 As might be expected, tbe nnmbers are very variable. Tbe relative 

 amounts of free and organic ammonia added by the fish to the water 



