CHANGES IN KNVIRONM KNT OF DAPHNIA MA(iNA. 221 



About a cubic centimetre of the couceutrated solution was 

 injected liypodevinically into a frog, but without any marked 

 effect. 



The remainder of the water which had been filtered, and 

 had been kept for a month in a bottle plugged with cotton 

 w^ool, was put into two beakers, and Daphnia were placed in 

 them. The animals grew and reproduced in a normal way. 

 Thus the poisonous nature of the water had apparently 

 passed off. 



All that can be said at present is that — 



(1) Daphnia living in a small confined volume of water 

 with plenty of food and oxygen gradually become unhealthy, 



■their spines diminish in length, and reproduction ceases. 

 After a prolonged period they die. 



(2) This water is injurious, though not as a rule fatal to 

 fresh Daphnia; the reproductive power, however, is very 

 quickly acted upon. 



(3) Cyclops and Cypres were observed living in the water 

 apparently without hurt. This fact would almost seem to 

 indicate that the water becomes specifically injurious to 

 Daphnia. 



(4) The injurious nature of the water seems to pass off 

 after a sufficiently long period. 



In a considerable volume (10 — 40 litres) of water the 

 phenomena observed are slightly different. On stocking the 

 aquarium, say with a dozen Daphnia, after a month or six 

 weeks with favourable conditions of tempei\ature and food 

 several hundred animals may be produced. Then quite sud- 

 denly something appears to happen, and the greater number 

 die, young and old alike. A few, perhaps thirty, survive. 

 These will live for months without producing eggs. After a 

 very considerable time eggs are formed, and the Daphnia may 

 become fairly plentiful again, but this second swarm is never 

 so great as the first. 



Considering the course of events in a small volume (200 

 c.c.) of water, we may perhaps interpret the above pheno- 

 mena in the following way. 



