AND OF PRODUCTS OF METABOLISM. 297 



were diminished in size. In ten experiments the aver- 

 age diminution was 7.1 per cent. It was concluded, 

 therefore, that the first batch of larvae had excreted 

 some products of metabolism into the water which had 

 adversely affected the growth of the second batch. 

 Other observations* showed that the growth of larvae 

 may be affected by their own metabolic products. Thus 

 it was found that the arm lengths of the larvse became 

 smaller and smaller the larger the number of larvae al- 

 lowed to develop together in a given volume of water. 

 In the accompanying table are given the mean results 

 of 159 sets of measurements, each on the anal and oral 

 arm lengths of 50 larvae. 



Here we see that when less than 1500 larvae were devel- 

 oping together, their relative anal and oral arm lengths 

 were respectively 121.2 and 118.4. As the number in- 

 creased, the lengths steadily dwindled down, till with 

 over 30,000 per litre they became reduced to respect- 

 ively 56.6 and 68.5, or about half their original amount. 

 Now it was found that the body lengths of the larvae, 



*Phil. Trans. 1895, B. p. 603. 



