The Relations between Marine Animai and Vegetable Life. 411 



in most cases produce» also a decrease in the body length, this 

 amounting on an average to 4.4^. In the two instances in which 

 the water was fouled by Arbacia and by Dorocidaris^ a positive 

 effect was produced on the body length; but nevertheless, the arm 

 lengths were negatively alfected. The results obtained with water 

 fouled by putrid Echinoids are not quite parallel for the arm and 

 body lengtbs. Thus in only one out of the five experiments made 

 was there a decrease in the arm leng-ths, whilst in three out of the 

 five there was a decrease of body length. There is in fact an average 

 inerease of 6.1^ in the arm length. but an average decrease of 

 \.\% in the body length. Again, the results obtained with Plutei- 

 fouled water are also rather irregulär. Thus in two out of the five 

 experiments made there is a pronounced positive effect on the arm 

 lengths, so that on an average the diminution is only \.%%. The 

 body lengths on the other band were in every case afifected un- 

 favourably, the average diminution being 5.0^. As a whole, however, 

 these results show plainly that whatever effect may be produced in 

 the body length by the fouled water, be it either positive or negative, 

 a sìmilar but more marked effect is produced in the arm length. 



The few experiments made with salts are also included in this 

 table, and they more or less confimi this conclusion as to similarity 

 of etfect. Thus in the experiments made with respectively ammonium 

 Chloride, potassium nitrite, and potassium nitrate, the average Varia- 

 tion in the length of arm is — 24.1^, +7.1^ and 4-3.1^, and in 

 the length of body respectively — 13.1^, — 3.4^ and + .5^. The 

 unfavourable effect of the ammonium chloride on both the arm and 

 the body lengths is thus very striking; but nitrites and nitrates, in 

 small quantities, probably bave little or no efiect on either. 



Finally, in the last line of the table, are given the effects pro- 

 duced by aeration of the water. In every case a distinctly favourable 

 effect was produced, this amounting on an average to \1.^%. This 

 is a mudi greater effect than that produced on the body length, 

 which amounted on an average to only .^%. It is presumably due 

 directly to the increased aeration, as the bacteriological observations 

 made did not show much change in the numbers of germs present. 



The Chemical and Physical Properties of Aquarium Water. 



In eaeh of the series of experiments made on larvai development, 

 the Aquarium water in which the fertilised ova were placed was 



