394 H. M. Vernon 



In this table the arrangement is the same as in the preceding 

 one, except that as a rule the composition of the fouled water was 

 determined after the larvpe had grown eight days in it, and not 

 before the addition of the fertilised ova. In Expts. 46 and 48, 

 however, the fouled water itself was analysed. 



Of the first eight experiments in this table, in which as usuai 

 the ova of Strongylocentrotrus were employed, we see that in only 

 two cases was a positive effect produced on the larv?e. In every 

 experiment with water fouled by the sea-urchins Strongylocentrotus, 

 SphcBrechinus or Echmus^ a pronouuced diminution in the size of the 

 larva? resulted. This diminution varies from 2.6 to 15.0^, it being 

 on an average 6.9^. On the other band a positive effect is produced 

 on larvai growth by the excretory products of Arbacia and Dorocidaris. 

 It would seem as if the negative or positive effect produced by the 

 products of excretion depended more or less on the morphological 

 relationship of the fouling animai. Thus on an average in the 

 three experiments with the water fouled by Strongylorentrotus^ 

 the effect produced, calculated per lOOgrams weight of animai per 

 litre per hour, is 3.4^. On the other band in the two experiments 

 with the water fouled by Spliceredàmis^ the average diminution is 

 only \A)h%. 



In Order to obtain further evidence as to the special fouling 

 effect of an animai on its own larvse, a few experiments were made 

 with other plutei, namely those of SphcerecMnus and Echinus. These 

 were killed and preserved after eight days' growth, in the same way 

 as the Strongylocentrotus larv^e. In Expts. 12 and 13, with Sphcer- 

 echinus larvse, very little effect was produced, but such as it is, it 

 lends Support to the other results obtained. In Expts. 21 and 22, 

 the plutei of Echinus were used. Here also a more adverse effect 

 is produced by the excretory products of Echinus, than by those of 

 Strongylocentrotus. The reciprocai ex[)eriment, with Strongylocentrotus 

 plutei, gave, on the other band, a contrary result. Thus in Exp. 18, 

 with water fouled by Echinus, the diminution is 5.4^, whilst in 

 Exp. 19, with water fouled by Strongtjlocentrotus , it is only 4.4^. 

 This single contrary result cannot be considered to balance the very 

 positive ones obtained with Strotigylocentrotus and Sphcer echinus, and 

 hence the existence of a special fouling effect of an organism upon 

 members of its own species may be recognised as highly probable. 

 A compari son of the numbers of ova reaching the larvai stage in the 

 various experiments is also in favour of this view. Thus of the 



