288 HIGH SCHOOL zoology. 



able hues of" the chania?leon and the tree-toad (which are ef- 

 fected reflexly through the nervous system), are to be expUuned 

 on the same principles. This does not exhaust its functions ; 

 it would appear with gregarious animals to be usefid in r ecog- 

 nition of other individuals of the same species, also for warning, 

 as in the case of the brilliantly coloured coral-snakes (E/aps 

 TV., 21). That such warning colours are not unfavourable to 

 their pcssessors, might lead us to suj^pose that the rattlesnake's 

 rattle (IV., 22) is a similar warning to enemies not to interfere. 



(7). Relation of Animals to Plants. 



2G. Some of the phenomena recounted above serve to i-ecall 

 that plants are not destitute of defences provided by natural selec- 

 tion in relation to phytophagous animals. Such ai'e the s})ines, 

 and the bitter, acrid aud poisonous excretions, such as tannin, 

 which the best protected possess. It is only in compai-atively 

 rare instances that plants can be said to assume the agressive, 

 and seize upon opportunities for securing food by absorption of 

 proteids from animals, instead of manufactui'ing them with the 

 aid of the nitrates of the soil. Such cases do occur in tiie 

 carnivorous plants, like the Venus' fly-trap ( Dionma), and the 

 more familiar pitcher-plaftts (Sarracenia) and sun-dew (Dros- 

 era). It must not be forgotten that tliei-e is a whole division 

 of the vegetable kingdom — the Fungi — which, being destitute 

 of chlorophyll, require to get their nourishment from previously 

 formed organic matter. They are either saproi)]iytic or paras- 

 itic forms, the latter sometimes so actively aggressive, as to be 

 one of the most fruitful causes of disease and death, both in the 

 animal and vegetable kingdoms. 



27. But there are also instances of plants and animals deriv- 

 ing mutual advantage from living together, which rec;dl the cases 

 of symbiosis of animals. Such ai-e afforded by the " yellow 



