Evolution of Animals 377 



(17) In both, asexual multiplication persists from the 

 Acaryota far up into the caryotic stage of evolution, and 

 frequently the entire historic structure of the organism 

 becomes locked up in one spore cell. Such spore cells 

 usually inherit from their acaryotic ancestry a much 

 greater degree of environal resistance than do the egg 

 cells. 



(18) In both, capacity is shown for hybridization, and 

 in correspondingly narrow and wide degree up to a def- 

 inite species- or at most genus-limit. 



(19) In both, as advancing evolution of tissues proceeds, 

 like protective, conducting, connecting, elaborating, di- 

 gestive, glandular, hair-forming, strengthening, and irrito- 

 contractile tracts or areas arise. 



(20) In both, like substances or functions may often 

 appear and again disappear, or be absorbed according as 

 en\dronal stimuli act or cease to act. 



(21) In both, physiological disuse of elaborating tissues 

 is gradually followed by morphological degeneration, and 

 often by death of the individual and of the group. 



The differences are: 



(1) Plants have gradually evolved, from primitive color- 

 less ancestors, etiolin and chlorophyllin, so they have 

 become autotrophic, in that they build up complex organic 

 from inorganic products. 



Animals seem to have evolved from a plant line in 

 which non-formation of the chlorophyll caused them to 

 depend on the plant world for elaboration of primary 

 organic food products. 



(2) Plants have usually a gelatinous or cellulose wall, 

 rarely one in which nitrogenous compounds are present. 



Animals have a nitrogenous cell wall when such is 

 present. 



(3) Plants are sedentary, except in some simple groui)s. 

 Animals are rarely sedentary, usually actively motile. 



(4) Plants respond very or rather sluggishly to envir- 

 onal changes. 



