326 



ZOOLOGY. 



without light there would be no life. Were it not for the 

 stimulus of light animals would be eyeless. Light ap[)ears 

 .^ t> to serve as an excitant in resjiiration. 



Heliotropism, so frequently observed iu 

 plants, also occurs in the animal world. 

 Infusoria press to the light and collect in 

 glass vessels on the side next to the 

 strongest light. It is so with Hydra., 

 Fig. .337, -Two Lim- starfish, and certain larval starfish. Slugs 

 reared in equal almost always move witli reierence to 

 (4°oo"cJbic c™u- giiivity and strong light, moving iu 

 ^eir^in a'bouTe straight lines vertically either from or 

 6 centimetres in towards the lio'ht. The daily migration of 



diameter; o, one ^ Jo 



reared in a flat pelaoic animtTls to the surface is thouoht 



vessel 23 centime- i- ^ o 



tres in diameter, by Grooiu and Loob to be due to hcliotro- 



Nov., 1890, to Feb., -f ,i ii , .i i -, i j^ n 



1831. After De pism ratlier than to tlie hotter water oi the 



"^"^' surface, though this may he questiotied. 



The "chromatic function" is that adaptation of color of 



fee ft 



■Ml ^W 





Fig. 338,— Chromatophores from the skin of a froj;. a, ■wholly contrnctefl; b 

 and c. half relaxe(i; '/, wholly lelaxei.!; p, wliolly conti'ncled — a capillaiy 



vessel; /, <i, h, exitaiKled (.•olm-cflls or clii'oinatnphorH.-;, Afti-r Listfr. 



the skill of the frog, chameleon, squid, fisli, crustaceans, 



