534 ON INCREASE IN SIZE [pt. iii 



increasing age. Lessona and Camerano brought forward field evidence 

 which agreed with the controlled results of Yung, who was later 

 confirmed by Perna and by Chiarugi & Livini. Yung also found 

 that the eggs of Salmo trutta hatched i day earlier when kept in the 

 light than when kept in the dark, and that the eggs of Limnaea 

 stagnalis, the pond snail, hatched in 27 days in the light but 33 days 

 in the dark. Davenport, following earlier speculations of Millet and 

 Blanc, has commented upon the regularity with which developing 

 embryos are hidden away from the light either in the egg or in the 

 uterus, but as this is not the case with animals such as the echino- 

 dermata there seems no great significance in the idea. Bodine and 

 Carothers have observed a marked inhibitory effect on embryonic 

 development of certain orthoptera [Melanoplus differentialis, Chorto- 

 phaga viridifasciata, Circotettix verniculatus) of direct sunlight (not the 

 heat accompanying it) and Miyakawa affirms the same for Schistoso- 

 mumjaponicum*; but, on the other hand. Page, taking like precautions, 

 reported that shad eggs could be made to hatch 12-15 hours before 

 the controls by allowing direct sunlight to fall upon them. Ruffini's 

 curious observation that the eggs oiBufo vulgaris in their jellies always 

 orient themselves with their animal poles pointing toward the light has 

 never been confirmed, but may have significance. According to Good- 

 rich & Scott light has no effect on chick embryo cells growing in vitro. 



Other researches have been made with the object of identifying 

 the most active wave-length. Beclard very early placed the eggs of 

 Musca carnaria behind screens of different colours, and found that 

 the embryos in the green light were the least developed after a 

 definite period, the rest following in the order, yellow, red, blue 

 and violet, in which last light they developed most rapidly. The 

 retarding effect of the green was also observed by Schnetzler. 

 Davidson's results are untrustworthy. 



Very striking effects were observed by Yung, whose papers are the 

 most often quoted : 



Length of tadpoles 



* See also the work of Frederich & Steiner. 



