398 



H. M. Vernon 



In the eight experiments here given, the larvse on an average 

 were diminished 6.9^^ in size. Probably the unfavourable influence 

 would bave been still more marked, if the water used had not been 

 filtered through asbestos to remove the larv» in it. Thus it was 

 only subsequent to the time these observations were made that such 

 filtration was found to bave so powerful an influence ou the 

 physiological qualities of the water. In that the water was always 

 filtered in the same manner, these experiments are, however, strictly 

 comparable amongst themselves. As regards individuai experiments, 

 especially with reference to , reciprocai' fouling, no complete set of 

 larvai measurements was obtained. Thus in Exp. 32, in which the 

 larvte of Strongyloceiitrotus were grown in water previously fouled 

 by larvai of the same species, the diminution in size is 4.5^, as 

 against a diminution of 3.3^ when some of the same larv« were 

 grown in water fouled by Echinus larvie. When, on the other band, 

 Echinus larv« were grown in specimens of the same water, those 

 in the Siroiiffi/locentrotus-foiüed water were diminished by 5.7^, and 

 those in the Echinus -fouled water failed to reach the eight days 

 larvai stage at all. This result would seem, therefore, to entirely 

 favour the couclusion that the excretory products of an organism are 

 more injurious to itself than to other organisms; but the other 

 observations made do not agree with this view. Thus in Exp. 30, 

 the larvai of Echinus, when grown in Echinus -fouled water, are 

 diminished in size by 11.6^, but, grown in Sfro?iffylocentrotus-fou\ed 

 water, by 13.3^. The attempt to grow Strongyloceiitrotus larvai in 

 these specimens of water was in both instances unsuccessful. Again, 



