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the plants. Since this was wi-itten some experiments have 

 been made which point to the conjecture being correct. At 

 the present time I am engaged Avith the subject, but the 

 following results seem to be appropriate here. 



Newly hatched Daphnia were placed in five glass capsules, 

 each of which was put in a shallow box. 



The first box was covered by a sheet of ground glass.^ 



Second box by a flat glass dish containing a solution of 

 fuchsin in spirit. (Spectroscopically a pure red.) 



Third box by a sheet of Chance's pot-green glass (trans- 

 mitting a trace of blue green). 



Fourth box by (1) a sheet of cobalt-blue glass, on the 

 top of which was placed (2) a flat glass dish containing a 

 diluted solution of ammoniated copper sulphate (perhaps 

 transmitting a trace of red). 



Fifth bos was made light-tight. 



Two broods of Daphnia were taken, and an individual from 

 each brood was placed into each glass capsule. Thus there 

 were two individuals derived from two broods in each cap- 

 sule. 



A second series of chambers was prepared, and three in- 

 dividuals from three broods were placed in each pot. The 

 animals Avere constantly supplied with fresh Avater and mud. 

 After a certain period the animals Avere measured by an ocular 

 micrometer; the dimension taken was the total length of the 

 body excluding the spine (see fig. 3, a, b). 



The results of the experiment are given in the following 

 table : 



^ With two pieces of grouiul glass the intensity of the white light is very 

 much reduced. The effect on the Daphnia, however, was practically the 

 same, hence the results observed are not simply due to the varying intensity, 

 but to the wave-length of the light. 



