88 THE INFLUii-NCE OF INANIMATE SHEROUNUINGS. 



ento-parasites are quite, or almost quite, white, appears a 

 striking proof of the accuracy of this statement. Even as 

 lately as 1870 it was asserted by the celebrated French depute 

 and physiologist, Paul Bert, that the hwvse of the well-known 

 Axolotl (fig. 24) were incapable of forming jjigment when they 

 were brought up under the influence of yellow light, and he 

 unhappily designated this absence of the epidermal pigment 

 as ' etiolation.' This term, as is well known, has a fixed signi- 

 fication in the physiology of plants; it is exclusively used to 



F)G. U.—Siivdon pisciforme, the Mexican A.xolotl. 



designate those cases of the absence of the green hue in plants 

 ^\liich, having grown in the dark, have been checked in the 

 formation of the chlorophyll-bodies, which ai'e the organs by 

 which they assimilate and elaborate their nutrition " at the 

 same time, as the light is no longer able to act as a check on 

 their excessive growth, the leaves and stems become much 

 elongated and acquire a yellowish-white hue, all of which phe- 

 nomena can be easily observed in the shoots and leaves of 

 potato tubers which have begun to sprout in a cellar. In the 

 cases of so-called ' etiolation ' described bv Bert as occurrin<r in 



