III. 4 LIGHT 95 



were, however, less differentiated, for they did not acquire their 

 hind legs so soon as did those in the white light. It may be 

 mentioned, however, that when the tadpoles reared under these 

 conditions are replaced in ordinary light and starved, those from 

 the violet exhibit a greater power of resistance. 



Experiments with Rana escnlenta gave the same result. In 

 this case the effect of darkness was also tried and found to be 

 distinctly unfavourable. Thus after one month the lengths in 

 darkness and white light were respectively 19-66 mm. and 

 23-10 mm., the breadths 4-66 mm. and 5-50 mm. ; after two 

 months the difference was intensified, the lengths being 21-50 mm. 

 and 32-16 mm., the breadths 7-16 mm. and 7-66 mm. The death- 

 rate in the dark was exceedingly high. 



The eggs and embryos of the Trout were likewise found by 

 Yung to be highly sensitive to green and red light, while the 

 larvae reared in violet hatched out rather more quickly than 

 those from yellow, blue, or white light. 



In an experiment on the eggs of Limnaea stagnalis, due to the 

 same investigator, the effect is measured by the time required 

 for the young to hatch out, as the following table shows : 



TABLE XI 

 Light. Time to hatching in days. 



Red 36 



Yellow . 25 



Green 



Blue 



Violet 



White 



Dark 



The heart is formed, Chen death occurs. 

 19 

 17 

 27 

 33 



Green light is evidently fatal ; development is retarded in red 

 light, less so in darkness ; yellow has about the same effect as 

 white light, while there is a considerable acceleration in blue and 

 violet. 



The relative effect produced by the various lights is as in the 

 preceding experiments. 



The results obtained by Vernon for Echinoid larvae are, 

 however, not quite consonant with this, as may be seen in the 

 table (Table XII), where the colours are arranged in the order 

 of the effect they produce. It will be observed that yellow is 



