456 Proceeclmgs of the Royal Physical Society. 



That light may influence animals quite apart from their eyes 

 has been repeatedly shown, especially by Plateau (161a, 162) ; 

 many tracheate Arthropods are indisputably " dermatoptic." 

 Some other influences of light are noted in the bibliography. 



In relation to plants, light is well known to have a yet 

 more important and very varied action, e.g., on the inter- 

 change of gases, on the disposition of chlorophyll, on the 

 direction, expanse, and distribution of leaves, on the number 

 of stomata, on the histology of the leaf, on plant movements, 

 and so on (141-143, 148, 160, 166, 167, 172-175, 177, 179, 

 180). Light is even a factor in variations of reproduction 

 among algse, e.g., in Botrydium. It is now a familiar fact 

 that strong sunlight, and not heat, is the most potent and 

 universal antagonist of germs. 



The absence of light stimulus can hardly be denied to 

 have a share in the degeneration of animals living in dark 

 regions (146, 147, 158, 159, 168, 170; cf., however, 178). 

 Darkness is unfavourable to the development of some cater- 

 pillars, and also influences tadpoles (154, 155, 181-189). 

 Schneider (168) has recently noted that subterranean condi- 

 tions tend to produce reversion to young or embryonic 

 conditions. According to Strethill Wright, polypes of the 

 higher Acalephae kept in darkness multiply abundantly by 

 buds only, while in the light and with insufficient supplies 

 of food, they bring forth Medusae. Finally, it may be noted 

 that minus light is said (149) to favour the production of 

 male, as opposed to female inflorescence on the shaded 

 branches of conifers. 



(c.) Electrical and Magnetic (190-196). — Electrical and 

 magnetic influences have also been recorded, but as their 

 rationale seems too hopelessly remote, I shall simply refer to 

 the instances noted in the bibliography, and especially to the 

 elaborate researches of Erommann (190). 



IV. Animate Environment. 



(Bibl., 197-205.) 



Animals may be influenced by fellow organisms indirectly 

 through the inanimate environment, but they may also be 



