SCORPIONS, SPIDERS AND CRABS 239 



supposed that this " music " serves the purpose of a 

 lure, or acts as an excitant, to the female, even though 

 inaudible to human ears. But there are many people 

 who are unable to hear the shrill squeal of our native 

 bats. Yet no one doubts but that all bats hear it. 

 The argument as to the absence of any sense of hearing 

 in certain Spiders is based on their failure to respond to 

 th?e vibrations of a tuning-fork, but this evidence is not 

 conclusive. Neither is it safe to infer that the presence 

 of stridulating organs in the adult and immature stages 

 of both sexes, in some species, precludes their recognition 

 as secondary sexual characters. They may serve the 

 double purpose of sexual excitants and terrifying enemies, 

 their motive being expressed by the quality of the sound 

 as certainly as the timbre of the human voice may express 

 rage or pleasure. 



Neither Spiders nor Scorpions exhibit any very striking 

 secondary sexual characters. As a rule the female is the 

 larger, often strikingly so. Bright colours are rare, and 

 are met with only among the Spiders, wherein sometimes 

 the male, sometimes the female, is the more resplendent ; 

 where bright colours — apple-green, red and yellow — do 

 occur, they seem rather to be of the type known as Anti- 

 cryptic, or aggressive resemblance colours. That is to say, 

 they are hues developed to deceive prey by reason of 

 the likeness they afford the wearer to its surroundings. 

 Thus, for example, one of our native Spiders {Tibellus 

 oblongus) is straw-coloured, and has an elongated body, 

 which is therefore seen with difficulty amid dry grass 

 and rushes which are the haunts of the species. Misumena 

 vatia, one of the Crab-spiders, resembles the flowers on 

 which it is accustomed to lurk for its prey. It is of a 

 variabk hue, commonly yellow or pink, and a favoured 



