298 Animal Life and Intelligence. 



described as tactile or olfactory in the lower invertebrates 

 are so described on a somewhat slender basis of evidence. 

 The sense-value of the bright marginal beads of sea- 

 anemones is unknown. Even in animals as high in the 

 scale of life as fishes, there is a complete set of sense- 

 organs the muciparous canals, in the head and along the 

 lateral line down the side, the function of which we can 

 only guess. By some they are regarded as olfactory ; by 

 others, as fitted to respond to vibrations or shocks of 

 greater wave-length than the auditory organ can appre- 

 ciate ; by others, as of importance for the equilibration or 

 balancing of the fish. 



It will thus be seen that, apart from the possibility of 

 unknown receptive organs as completely hidden from 

 anatomical and microscopic scrutiny as the end-organs of 

 our temperature-sense, there are in the lower animals 

 organs which may be fitted to receive modes of influence 

 to which we human folk are not attuned. 



And what are the physical possibilities ? We have seen 

 that, through the telaesthetic senses hearing, vision, and 

 the temperature-sense we are made aware of the vibra- 

 tions of distant bodies, the effects of which are borne to us 

 on waves of air or of aether. The limits of hearing with us 

 are between thirty and about forty thousand (or perhaps, 

 in very rare cases, fifty thousand) vibrations per second. 

 But these are by no means the limits of vibrations of the 

 same class. By experiments with sensitive flames,* Lord 

 Rayleigh has detected vibrations of fifty- six thousand per 

 second ; and Mr. W. F. Barrett has shown that a sen- 

 sitive flame two feet long is sensitive to vibrations beyond 

 the limit of his own hearing and that of several of his 

 friends who were present at the experiment. We have 

 some reason to suppose that vibrations too rapid to be 

 audible by man are audible by insects, but not much is 

 known with regard to the exact limits. 



The following table shows what is known concerning 



* The observations are not yet published, and I have to thank Lord 

 Rayleigh for his courtesy in allowing me to make use of this fact. 



