ii8 ANIMAL BEHAVIOUR 



perhaps blending into general sensation in the lower in- 

 vertebrates. 



Taste. Gustatory organs. Very similar to smell. 

 Touch. The tactile organs in the skin. 

 Heat and Cold. Receptor organs in the skin. 

 Sexual Feeling. Receptors in the external genital organs. 

 in. Associated with the intero-ceptors. 



Hunger, Thirst, Nausea, Distension. Receptors in the 

 walls of the alimentary canal. 



Heart-panic. Receptors in heart, pericardial cavity and 

 possibly arteries. 



Visceral Pain. Receptors in the muscles of the alimentary 

 canal. 

 iv. Associated with the proprio-ceptors. 



Muscular Sense, Pressure, Weight, Effort. Receptors 

 in the muscles and joints. 

 Rheumatic Pain. The same. 



Vertigo, Balance, Directional Sense. Receptors in 

 the internal ear. 

 The classification is necessarily an obscure one and we are 

 hopelessly shut off from ever knowing, with any probability, the 

 sensations of animals other than man. And even the nature of 

 some sensations may be communicable between man and man 

 only imperfectly — as in the notion of normal colour sensation 

 that may be acquired by a colour-blind man. The list must be 

 regarded as merely indicative of the kinds, or qualities, of sensation 

 had by normal human animals. 



And it is seldom, or never, that we have such a single quality 

 of sensation unmingled with others. We come by the rude 

 classification by acts of attention. We exercise mental analysis, 

 assisted by experimental devices and then we '* proceed to the 

 limit " and arbitrarily isolate from their sensational context each 

 pure, or indefinable quality. No one such sensational quality 

 can be described in terms of any other — seeing has nothing to 

 do with hearing, redness with blueness, heat with cold and so on. 

 " Colour-tone," etc., are only terms used to express rough 

 analogies. 



43^. Nervous Energies. It is, of course, an insoluble pro- 

 blem why the nervous impulse proceeding from, say, a visual 

 receptor may be accompanied by the sensations of light and colour 



