414 H- M. Vernon 



.145, .142, .173, .222 and .247 mgm. of free ammonia, and .098, .116, 

 .127, .185 and .193 mgm. of organic ammouia to be present. 



There seems to be a relation between the amouuts of organic 

 ammouia present in the water, and the percentages of fertilised ova, 

 which, on development in this water, reached the eight days' larvai 

 stage. Thus in the five experiments in which 52^ or less of the 

 ova reached full larvai development, the organic ammonia present 

 amounted on an average to .166 mgm., whilst in the remainiug eleven 

 experiments, in which 63^ and upwards developed, it averaged only 

 .131 mgin. The values for the free ammonia were respectively .221 

 nnd .219 mgm., or practically the same. 



The two sets of ammonia values in the table which are enclosed 

 in brackets, are for water drawn oif through one of the taps, and 

 not taken from the large tank of the Aquarium. The ammonia present 

 is considerably smaller in their case, though of course the specific 

 gravity is unaltered. 



Practical Conclusions. 



Thus far only the experimental work itself has been described 

 and discnssed. What are the practical applications of the conclusious 

 arrived at, especially with regard to the maintenance, in as efficient 

 a manner as possible, of marine aquaria on a large scale ? To con- 

 sider the results in the order already described, we have seen that 

 algse, both green and red, if they cau be kept in a healthy condition, 

 may exert a considerable purifying influence on the water. There 

 is no fear that in a marine aquarium the vegetable life will ever 

 outweigh the animai, and hence as many and as varied weeds as 

 possible may be introduced. Thus the green weed Caulerpa has 

 recently bcen introduced into one of the tanks at the Naples Aquarium, 

 and appears to be living healthily. Ulva also keeps in good con- 

 dition, but red weeds are apparently unable to flourish for any length 

 of time. Probably the water itself is initially too impure for these 

 weeds to have a chance of growing, but if the water could once be 

 obtained in a purer coudition, there seems to be no reason why they 

 should not grow in it, and help to maintain the higher standard of 

 purity. As previously mentioned, Warington found that these red 

 weeds thrived best when placed in a very dull light, and the few 

 observations raade on the subject confirmed this conclusion. Thus 

 several species of red weed, introduced into a very dimly illuminated 



