396 



H. M. Vernon 



be one of the important factors, aud lieuce a few experiments were 

 made lipon the effects of water fouled by dead sea-nrchins, in order 

 to test this supposition. In that tlie fouling effected by a decomposing 

 organism is so very much greater than that of a living one, the 

 water was exposed to the contaminating agent for only a very 

 few minutes. The results obtained are given in the aecompanying 

 table. 



Here we see that in two out of the five experiments a positive 

 efifect, amounting on an average to 2.0^, was produeed, and in the 

 remaining three, a negative effeet averaging '0.1%. In the first ex- 

 perimeut, made in warm weather with a rapidly decomposing sea- 

 urchin, a positive influence was exerted, in spite of the cousiderable 

 eontamination of the water which the chemical analysis proved. In 

 one of the last two experiments, in which the water was fouled by a 

 Sphrereclmms killed three days previously by a short immersion 

 in fresh water, some of the fouled water thus obtained was diluted 

 with normal sea-water. Both with the diluted and the undiluted 

 water, a cousiderable reduction in the size of the larvae was 

 brought about, this reduction being proportional to the amount of 

 products of putrefaction present. In the other pair of experiments, 

 made with two Strongylocentrotus individuals, also killed three days 

 previously, the slight negative effeet produeed by the conceutrated 

 fouled water was converted into a positive one on dilution. On the 

 whole therefore it would seem that, in small quantities, even the 

 products of putrefaction of an organism may have a favourable efifect 

 on larvai growth. The fact that on an average no less than %^% 

 of the fertilised ova used in these experiments reached full larvai 

 development, Supports this view. It should, however, be pointed out 



