610 Causes and Course of Organic Evolution 



})asis, of complicated cogitic as well as simpler life conditions, 

 we can now consider various animal acts which by analysis 

 may yield a key to mental processes. Here we would again ac- 

 cept it that, starting with plants and their irritotactic relations, 

 viz., heliotaxy, geotaxy, hydrotaxy, thigmotaxy, paraheliotaxy, 

 chemotaxy, thermotaxy, and electrotaxy, the same sense rela- 

 tions — no more and no less — characterize animals, if we except 

 that to animals the auditory or tonotactic sense is superadded. 

 If, however, as already noted (p. 118), we regard the tonotactic 

 as a highly evolved state of the thigmotactic sense, plant and 

 animal senses in environal relation would agree. 



But in animals some of these become greatly concentrated 

 into condensed and highly sensitive absorbers, as, for example, 

 the eyes for the heliotactic sense, the nose for the chemotactic, 

 and so on. Such animals as Hydra (200: 413), Eudendriiim 

 (60: 179), and others, however, exhibit a more or less diffuse 

 heliotropic and paraheliotropic response. 



From all the facts now before us the writer would conclude 

 that all sense-impressions wholly and primarily arise for each 

 organism from external stimuli, that are passed in through 

 some one or more of the sense areas. In the case of man we 

 can at least approximately picture to ourselves what a human 

 infant would become if at time of birth all the sense areas — 

 the eyes, nose, ears, touch-centers, etc. — over the body were 

 destroyed, and the infant were yet to live. Compared even 

 with the long recorded cases of infants reared in the silence of 

 solitary cells, its condition would be miserable, and it could 

 only grow up as an inert passive mass, even though living, that 

 absorbed no impressions, and that propagated only uncorre- 

 lated movements. 



Most naturalists and students of animal behavior now in- 

 cline — and we believe rightly — to put the beginnings of men- 

 tality low down in the invertel^rate scale, and we have already 

 suggested at or somewhat below the stage where ganglion cells 

 are first recognized. But in attempting to learn how cogitic 

 energy or mentality is exhibited in the lower animals we may 

 begin by selecting a case from amongst the worms. 



