SKNSA TION IN INSECTS. 497 



that which leads to the conclusion that they possess keen 

 powers of vision, smell, and touch. 



Pain. Evidence of a satisfactory kind indicates that pain is 

 by no means a phenomenon commonly exhibited by the lower 

 forms of life in any high degree; indeed, even in the human race 

 susceptibility to pain is far more developed in the higher than 

 in the lower races of mankind ; and the comparative indiffer- 

 ence to pain exhibited by some races of savages is notorious. 



Dominant Sensations. Just as in man the sense of sight, in 

 dogs that of smell, and in the timid herbivora the sense of 

 hearing are the most important, so there are insects in which 

 each of these senses is dominant over the others. I have 

 already drawn attention to the remarks of Forel on this subject 

 (p. n). In the Dragonflies, Libcllula, and the Diurnal Lepi- 

 doptera, the sense of sight is undoubtedly paramount; the rapid 

 hawking flight of the former is well known, and indicates the 

 keenest vision, and Belt (naturalist in Nicaragua, p. 108) gives 

 an instance of the manner in which some butterflies avoid the 

 webs of spiders indicative of highly developed visual powers. 

 He says : 



' A large spider (Nephila) builds strong yellow silken webs, 

 joined one to the other, so as to make a complete curtain of 

 web, in which were entangled many large butterflies, generally 

 forest species, caught flying across the clearing. I was at first 

 surprised to find that the kinds that frequent open places were 

 not caught, although they abounded on low white-flowering 

 shrubs close to the webs ; but on getting behind them, and 

 trying to frighten them within the silken curtain, their instinct 

 taught them to avoid it, for, although startled, they threaded 

 their way through open spaces between the webs with the 

 greatest ease.' 



Hearing a Warning Sense. In mammals, hearing is frequently 

 a warning sense, more especially amongst those species which 

 are helpless against their enemies. According to Graber, the 

 Cockroach (Blatta Germanic a) is exceedingly sensitive to sounds, 

 especially in the dark, or when its eyes have been blinded. It 

 is familiar to all that children and timid persons are easily 



