410 



H. M. Venion 



in the normal, whilst on the eighth day they were considerably in 

 excess. 



Thus far we have seen only the efifects of purified water on the 

 arm lengths. In the following table are given the effeets of foiiled water. 



In seven out of the ten experiments niade with water fouled 

 by various animals, the arm lengths were increased in amount, 

 and in the other three, decreased. On an average this increase 

 amounts to 9.5^, or considerably more than the increase in 

 body length, which in these particular experiments amounted to 

 2.4 X- In the three experiments in which the arm lengths were 

 diminished, the foulness of the water, as judged by the amounts of 

 free and organic ammonia present, was greater than in any of the 

 other instances. Very probably therefore, if the fouling had not been 

 carried to so great a degree, a positive eflfect would have been 

 produced as in the other experiments. The animals producing this 

 fouling were fish, crabs, and a herniit crab with three anemones. In 

 the eight experiments made with water fouled by Echinoids, an un- 

 favourable effect on the arm length was exerted in every case but 

 one. The average diminution in size was 9.4^, or a similar vaine, 

 only in the opposite direction, to that obtained with animals other 

 than Echinoids. As we have already seen, Ecbinoid- fouled water 



