156 Mr. H. M. Vernon. The Relations betiveen 



as from the theoretical standpoint of the changes taking place under 

 natural conditions in the open sea. 



The method of investigation was a triple one, viz., chemical, physio- 

 logical, and bacteriological. The chemical procedure consisted in 

 carefully determining the free and albuminoid ammonia present in 

 the various specimens of water by means of the well-known method of 

 Wanklyn, Chapman and Smith. In certain cases also the nitrites 

 were determined by the metaphenylenediamine reaction. The water 

 was tested physiologically by allowing the fertilised ova of the sea- 

 urchin, Strongylocentrotus lividus, to develop in it, and by determining 

 the change produced in the size of the larvae after eight days' 

 growth under various conditions. The larvae were in each case 

 measured under the microscope in groups of fifty. In addition also 

 the proportion of ova arriving at the eight days' larval stage was 

 always determined. The bacterial quality of the water was tested by 

 counting the number of colonies obtained by gelatin plate culture. 



With reference to the purifying effects of vegetable life on the water, . 

 it was found that green weeds such as Ulva, will, when placed in 

 Aquarium tank water, rapidly remove the free ammonia present, 

 though they slowly increase the albuminoid ammonia. Thus in one 

 case 62 per cent, of the free ammonia was removed after two days, 

 and 95 per cent, after ten days, whilst the albuminoid ammonia was 

 increased by respectively 22 per cent, and 27 per cent. If the water 

 be in addition exposed to sunlight, the free ammonia is removed less 

 rapidly than before, but the albuminoid ammonia increased more 

 rapidly. Sea-urchin larva? grown in water thus purified are, as a rule, 

 increased in size, this increase being in one case 14'4 per cent. Larvae 

 allowed to develop in direct contact with the alga were, as a rule, 

 found to be slightly diminished in size, although analyses of the 

 water made at the end of the experiments showed that the albuminoid 

 ammonia had been appreciably diminished, as well as the free 

 ammonia. It would seem, therefore, that the alga is able to absorb 

 the albuminoid ammonia when it is present in considerable amount. 

 The proportion of fertilized ova developing to the full larval stage 

 was considerably greater in these experiments than when no alga had 

 been added to the water, hence the effect of the weed would seem on 

 the whole to have been a favourable one. 



Red weeds, such as Gelideum, when kept in Aquarium water, cause 

 a considerable increase in the albuminoid ammonia, and as a rule 

 also increase the free ammonia. Larvae grown in water thus treated 

 are diminished in size, but when allowed to develop in direct contact 

 with smaller quantities of the weed, may be increased in size. Small 

 quantities of red and green weeds combined cause an increased 

 number of the ova to reach the larval stage, and may also cause an 

 increase in the size of the larvae. 



