Influence of Environment upon the Organism. 455 



at any rate, increase of heat must be regarded as a katabolic 

 condition. Various experiments have been made on the 

 adaptation of organisms to increased temperature (134), and 

 Dallinger's (116) recent elevation of monads from life at 65° 

 F. to life at 158° F. are particularly noteworthy. 



Cold has, of course, generally a reverse action, checking 

 activity, finally producing coma, diminishing the rate of 

 development, and tending to produce dwarf or even larval 

 forms (113, 115, 120, 132, 134, etc.). Laboulbene (126) notes 

 how low temperature and damp atmosphere may retard for 

 years the development of the embryo of Ascaris luinbrlcoides, 

 which normally requires only a month or so. Eeaumur's 

 classic experiments on aphides show that the cold of approach- 

 ing autumn is one of the conditions of the return of males ; 

 and various suggestive observations have been made on the 

 relation between temperature and sex (121, 124, 129, 133, 

 138). That alterations of climate in the past may have had 

 important modifying influences on organisms is extremely 

 probable, and Weismann (137) has given a full discussion of 

 this factor in reference to the seasonal demorphism of some 

 Lepidoptera. 



(5.) Light (140-189). — A beam of light shed on a giant 

 amoiba [Felomyxa) causes a shock-like shrinking, and a 

 general contraction is common among higher forms (144, 

 161). The majority of animals avoid strong illumination, 

 but not a few are as markedly light-seeking (150, 151, 152, 

 161). It is possible that some of the incipiently-eyed and 

 many-eyed lower animals may absorb solar energy, and 

 deserve the title " heliophagous " (158a). Light is believed 

 in some cases to affect the colours of animals (156), and this 

 seems demonstrable in the familiar instance of bird's eggs 

 (157). Yung has made an elaborate series of experiments 

 (181-189) on the influence of differently coloured light on 

 the development of tadpoles, while Poulton's beautiful 

 researches (168, 164, 165) on the influence of coloured 

 surroundings on insect larvse and pupse afford one of the 

 best illustrations of a very subtle environmental influence. 

 Heron-Eoyer (153) quickened the development of the larvse 

 of Bombinator by prolonging the conditions of daylight. 

 VOL. IX. 2 H 



