406 H. M. Vernon 



but No. 134, the above mentioned one in which open sea-watev was 

 used. It would tlierefore seem that the specimens of water used 

 must bave contained some more than usually powerfiil uitrifying- 

 organisms. 



Of the other observations made, only a few need be referred to 

 bere. Thus in an experiment in which .5615 gm. of potassium nitrate 

 per litre had been added to the water, only .207 mgm. N2O3 was 

 present after eight days' larvai growth, as against the .450 mgm. 

 present in the normal water. It would therefore seem that the nitrites 

 formed in the water are not due to a reduction of the nitrates which 

 happen to be present, but must be due to processes of oxidation. 



The nitrifying process seems unfavourably atfected by aerating 

 the water by violent shaking. Thus shaken water was found in two 

 experiments to contain respectively .067 and .243 mgm. ì^^^ò after 

 eight days' larvai growth, as against the .101 and .450 mgm. present 

 in normal water. 



With respect to the experiments on the fouling of water by 

 other organisms, it would seem that no increase in the nitrites is 

 present either before or after the growth of larva;. Thus water, fouled 

 by a putrid Sphcèrecldnus contained .100 mgm. N2 0;j, and that by 

 Strongylocentrotus^ also .100 mgm. The normal water before fouling 

 contained .121 mgm., and hence some immediate reduction of nitrites 

 must bave taken place. After eight days' larvai growth, the Sphrnr- 

 e<7/m^^^s- fouled water contained .252 mgm., and the other water 

 .360 mgm., as against the .450 mgm. present in the normal water. 



The Arm-Length Measurements. 



In addition to measuring the body lengths of the larvse, a second 

 measurement, that of the aboral or anal arm length, was made as 

 well. By this means it was hoped to derive additional Information 

 as to the phj^siological effects of the various specimens of purìtied 

 and fouled water. Thus, as has been shown with some detail in the 

 paper already referred to ', the arm lengths of the larva) are not by 

 any means always efifected to the same extent, or even in the same 

 direction, as the body lengths, on change of environmental conditions. 

 For instance, increased temperature during development causes a 

 diminution in the body length, and an increase in the arm length: 

 dilution of the water, an increased body length, and no efifect at ali 



1 ibid. pag. 601—612. 



