348 MENTAL EVOLUTION IN ANIMALS. 



precise ; for in some existing animals certain faculties are 

 more highly developed than they are in other existing 

 animals, which nevertheless with regard to their general 

 psychology occupy a higher level of mental evolution. There- 

 fore the faculties which I have named in the vertical column 

 have been chosen only because they serve as convenient 

 indices to mark the general upward progress of mental evolu- 

 tion in the animal kingdom. 



I have already sufficiently expressed my doubt as to the 

 levels at which all animals below the Articulata should be 

 placed, and I have explained that this doubt arises from the 

 difficulty, or rather the impossibility of ascertaining at what 

 grade of psychological evolution consciousness first occurs. 

 The positions, therefore, which I have assigned to the Coelen- 

 terata and Echinodermata are confessedly arbitrary, and have 

 been determined only because I have not been able to observe 

 that these animals give any unmistakable evidence of percep- 

 tion as distinguished from sensation. This remark applies 

 especially to the Ccelenterata, which in my opinion present 

 no semblance of evidence that any of their responsive move- 

 ments are of a perceptive, or even of a conscious nature. My 

 judgment with respect to the Echinodermata is less confident, 

 for although I am sure that I am right in placing them on a 

 higher level of sensuous capability than the Ccelenterata, I 

 am not at all sure that I ought not to have placed them one 

 stage higher (i.e., on 18 instead of 17), so as to have 

 brought them within the first rise of perception. For the 

 " acrobatic " and " righting " movements which are per- 

 formed by these animals, and which I have described elsewhere, 

 are, to say the least, strongly suggestive of true powers of 

 perception. It is, therefore, on the principle of preferring to 

 err on the side of safety that I have placed the Echinoder- 

 mata on level 17 and not on level 18. That I am justified 

 in attributing to these animals faint powers of memory (as 

 distinguished from the association of ideas) may, I think, be 

 shown by the fact that when a star-fish is crawling along the 

 perpendicular wall of a tank at the level of the surface of the 

 water, it every now and then throws back its rays to feel for 

 other surfaces of attachment, and if it does not succeed in 

 finding such a surface, it again applies its rays to crawling 

 along the side of the tank in the same direction as before, in 

 order that it may again and again repeat the manoeuvre in 



