590 REroKT— 1898. 



being transferred to the Oxford table during July, August, and September. 

 As it is scarcely possible to describe only those portions of the work I 

 was engaged upon when occupying the British Association table, I will 

 now furnish a brief report of the whole of the work I undertook during 

 my stay at Naples. 



In my last year's report I stated that I was investigating the condi- 

 tions of animal life in marine aquaria. I continued to work on this 

 subject for several months, and have embodied my results in a paper 

 which will shortly be published in the ' Mittheilungen aus der zoologischen 

 Station zu Neapel,' and which is entitled ' The Relations between Marine 

 Animal and Vegetable Life.' An abstract of the paper has already been 

 published.^ It is on this account unnecessary to describe the research in 

 any detail ; but I should like to take this opportunity of drawing attention 

 to the scope and practical bearing of the work, as it might thereby be brought 

 to the notice of some persons who are interested in the subject, but who, 

 judging from the title of the paper, might imagine it did not concern them. 

 Thus the original object of the work was to determine how the nitrogenous 

 matter excreted by marine animals into the water is removed, and what 

 parts the various forms of vegetable life and other agencies play in the 

 process. This subject is of interest from its practical bearing on questions 

 relating to the efficient maintenance of marine aquaria, whilst from the 

 theoretical standpoint it is of importance to our comprehension of the 

 changes taking place under natural conditions in the open sea. The 

 method of investigation was a triple one — viz., chemical, physiological, and 

 bacteriological. The chemical procedure consisted in determining the free 

 and ' albuminoid ' or organic ammonia present in the water by the well- 

 known method of Wanklyn, Chapman, and Smith. The physiological 

 procedure consisted in allowing the fertilised ova of the sea-urchin 

 {Strongylocentrotiis lividus) to develop in the various specimens of water, 

 and then, after eight days' growth, killing and measuring the larvae in 

 groups of fifty, in order to determine the changes produced in their size. 

 The bacterial quality of the water was tested by counting the number of 

 colonies obtained on gelatin plate culture. 



The three chief vegetable agencies concerned in the purification of the 

 water are — (1) the macroscopic algae ; (2) the diatoms and microscopic 

 algae ; (3) the bacteria. It was concluded that under natural conditions 

 in the open sea the bacteria form the most important of these purifying 

 agencies. Thus, as considerably the larger portion of the water of the 

 ocean extends to depths such that no trace of light can penetrate, it follows 

 that no chlorophyll containing organism can exert an influence on it. As 

 B. Fischer^ has shown, however, bacteria are everywhere present. Now it 

 was found that if the impure aquarium water was kept in darkness for 

 about three weeks, it might become as pure, in respect of the ammonia it 

 contained, as open sea water collected 10 kilometres from the shore. 

 Judged by the physiological standard, however, it was not nearly so pure. 

 Thus larvae grown in it were on an average only 7 '5 per cent, larger than 

 those grown in the impurified aquarium water, whilst those grown in the 

 open sea-water were 16-0 per cent, larger. In marine aquaria it seems 

 probable that bacteria play a considerable part in maintaining the purity of 

 the water, even though the water may be stored for but very short periods 



' Froc. Boy. Soc. vol. Ixiii. p. 155. 



^ ' Ergebnisse der Plankton Expedition der Humboldt-Stiftung,' Die Baliteiiende$ 

 Xeeres (Ed. iv. I\I.g.) 



